feat(calc,ui): complete tight-mode HEX entry with cross-base chaining and result formatting

- Add formatResultEntryForBase + update Equals/Mod/ChangeSign so committed results
  format in the active display base (e.g. HEX shows "C8", "1B0" not decimal).
- Robust per-line centering for dynamic A-F hexRow and keypad rows under display
  (prevents split key borders/decorations on bottom row).
- Updated test expectation for HEX result digits.
- Enables validated cross-base flow: DEC entry, Tab to HEX, continue op, see
  result in active base, Tab back converts displayed value correctly.
- style: gofmt -s all touched sources (ui_test.go, version_test.go etc.).
- ci: add lint and cross targets to Makefile.
  - cross produces the 6 platform binaries expected by release.yml on v* tags.
  - lint target for local parity (CI continues to use golangci-lint-action).

This is the v0.3.0 release-ready state (user-validated: 100 DEC -> Tab HEX +64 = C8 -> Tab DEC 200).

Makefile

@@ -1,4 +1,4 @@
-.PHONY: test test-short test-cover build install clean help
+.PHONY: test test-short test-cover build install clean lint cross help
 
 SHELL := /bin/bash
 
@@ -51,3 +51,23 @@ help:
 	@echo "  make test        - run all tests with race detector"
 	@echo "  make test-short  - short tests with race"
 	@echo "  make clean       - remove build/"
+	@echo "  make lint        - run golangci-lint (requires golangci-lint in PATH; CI uses action)"
+	@echo "  make cross       - cross-compile for linux/darwin/windows (amd64/arm64) for releases"
+
+lint:
+	@command -v golangci-lint >/dev/null 2>&1 || { echo >&2 "golangci-lint not found in PATH (install via 'go install github.com/golangci/golangci-lint/cmd/golangci-lint@latest' or rely on CI)"; exit 1; }
+	golangci-lint run ./...
+
+cross: deps
+	@mkdir -p build
+	@echo "Cross-compiling gralculator (VERSION=$(VERSION) COMMIT=$(COMMIT))..."
+	@for os in linux darwin windows; do \
+		for arch in amd64 arm64; do \
+			ext=""; if [ "$$os" = "windows" ]; then ext=".exe"; fi; \
+			out="build/gralculator-$$os-$$arch$$ext"; \
+			echo "  $$os/$$arch -> $$out"; \
+			CGO_ENABLED=0 GOOS=$$os GOARCH=$$arch go build -trimpath -ldflags "$(LDFLAGS)" -o "$$out" . || exit 1; \
+		done; \
+	done
+	@echo "✅ Cross builds complete:"
+	@ls -lh build/gralculator-* 2>/dev/null | cat || true

internal/calc/calc.go

@@ -189,7 +189,7 @@ func (e *Engine) EnterDigit(d rune) {
 	}
 
 	// Default (DEC): decimal digits only (validate to keep entry clean)
-	if (d >= '0' && d <= '9') {
+	if d >= '0' && d <= '9' {
 		if e.entry == "0" || e.entry == "" {
 			e.entry = string(d)
 		} else {
@@ -229,7 +229,7 @@ func (e *Engine) Equals() {
 	right := e.currentNumericValue()
 	result := e.applyPending(e.pendingLeft, right, e.pendingOp)
 	e.accumulator = result
-	e.entry = formatResultEntry(result)
+	e.entry = formatResultEntryForBase(result, e.base)
 	e.pendingOp = ""
 	e.pendingLeft = 0
 }
@@ -255,7 +255,7 @@ func (e *Engine) applyPending(left, right float64, op string) float64 {
 	}
 }
 
-// formatResultEntry produces a clean entry string for a committed result.
+// formatResultEntry produces a clean entry string for a committed result (DEC).
 func formatResultEntry(v float64) string {
 	if math.IsInf(v, 0) || math.IsNaN(v) {
 		return "0"
@@ -272,13 +272,40 @@ func formatResultEntry(v float64) string {
 	return s
 }
 
+// formatResultEntryForBase produces the result string formatted for the current display base.
+// For HEX/BIN/OCT this yields the appropriate integer digit string (so that FormatForDisplay's
+// raw-entry short-circuit for HEX and currentNumericValue's base-aware parsing both see correct
+// digits for the result). This makes results appear in the active base (e.g. 1FFE not 8190 in HEX).
+func formatResultEntryForBase(v float64, b Base) string {
+	if b == BaseDEC {
+		return formatResultEntry(v)
+	}
+	if math.IsInf(v, 0) || math.IsNaN(v) {
+		return "0"
+	}
+	i := int64(v)
+	if i < 0 {
+		i = 0
+	}
+	switch b {
+	case BaseHEX:
+		return strings.ToUpper(strconv.FormatInt(i, 16))
+	case BaseBIN:
+		return strconv.FormatInt(i, 2)
+	case BaseOCT:
+		return strconv.FormatInt(i, 8)
+	default:
+		return formatResultEntry(v)
+	}
+}
+
 // Mod performs immediate modulo using the current entry as the right operand
 // (useful for a dedicated MOD button that acts like = for modulo).
 func (e *Engine) Mod() {
 	right := e.currentNumericValue()
 	result := math.Mod(e.accumulator, right)
 	e.accumulator = result
-	e.entry = formatResultEntry(result)
+	e.entry = formatResultEntryForBase(result, e.base)
 	e.pendingOp = ""
 }
 
@@ -307,7 +334,7 @@ func (e *Engine) ChangeSign() {
 		return
 	}
 	e.accumulator = -e.accumulator
-	e.entry = formatResultEntry(e.accumulator)
+	e.entry = formatResultEntryForBase(e.accumulator, e.base)
 }
 
 // Backspace removes the last character from the current entry.

internal/calc/calc_test.go

@@ -274,8 +274,9 @@ func TestEnterDigit_HEX(t *testing.T) {
 	e.SetOperator("+")
 	e.EnterDigit('1') // simple commit
 	e.Equals()
-	if got := e.FormatForDisplay(); got != "432" {
+	// Result is formatted according to the current base (HEX), so 431+1 = 1B0 hex not decimal 432.
-		t.Errorf("after hex commit +1: want 432, got %s", got)
+	if got := e.FormatForDisplay(); got != "1B0" {
+		t.Errorf("after hex commit +1: want 1B0, got %s", got)
 	}
 }
 

internal/ui/ui.go

@@ -233,7 +233,7 @@ func (a *App) View() string {
 	numKey := keyStyle.Copy()
 	opKey := keyStyle.Copy().Foreground(lipgloss.Color("63")).Background(lipgloss.Color("235"))
 	clearKey := keyStyle.Copy().Foreground(lipgloss.Color("203")).Background(lipgloss.Color("52"))
-	modKey := keyStyle.Copy().Foreground(lipgloss.Color("214")) // orange-ish for MOD
+	modKey := keyStyle.Copy().Foreground(lipgloss.Color("214"))                                   // orange-ish for MOD
 	hexKey := keyStyle.Copy().Foreground(lipgloss.Color("214")).Background(lipgloss.Color("235")) // for A-F, only shown in HEX mode
 
 	makeKey := func(label string) string {
@@ -278,6 +278,34 @@ func (a *App) View() string {
 		hexRow := lipgloss.JoinHorizontal(lipgloss.Top,
 			hexBtn("A"), spacer, hexBtn("B"), spacer, hexBtn("C"), spacer, hexBtn("D"), spacer, hexBtn("E"), spacer, hexBtn("F"),
 		)
+		hexW := lipgloss.Width(hexRow)
+		// Robust per-line centering of the pre-joined 5-key rows under the 6-key hex row.
+		// We pad each individual line of the row block explicitly. This avoids any subtle
+		// artifacts from Style.Width+Align or PlaceHorizontal when the input is already a
+		// multi-line string containing ANSI border sequences. Ensures every line (including
+		// the bottom border lines of the last row) has exactly the same width so vertical
+		// borders and bottom edges line up cleanly with no dangling fragments or splits.
+		centerUnderHex := func(block string) string {
+			if block == "" {
+				return block
+			}
+			lines := strings.Split(block, "\n")
+			for i, line := range lines {
+				cw := lipgloss.Width(line)
+				if cw >= hexW {
+					continue
+				}
+				pad := hexW - cw
+				left := pad / 2
+				right := pad - left
+				lines[i] = strings.Repeat(" ", left) + line + strings.Repeat(" ", right)
+			}
+			return strings.Join(lines, "\n")
+		}
+		row1 = centerUnderHex(row1)
+		row2 = centerUnderHex(row2)
+		row3 = centerUnderHex(row3)
+		row4 = centerUnderHex(row4)
 		rawGrid = lipgloss.JoinVertical(lipgloss.Left, hexRow, row1, row2, row3, row4)
 	} else {
 		// Normal mode: standard 4-row grid (no A-F)
@@ -287,10 +315,24 @@ func (a *App) View() string {
 	// Center the key grid directly under the display.
 	// No enclosing container — just the individually styled keys.
 	// When in HEX the A-F row appears at the top of the keypad.
-	keypad := lipgloss.NewStyle().
+	// Explicit per-line centering of the entire rawGrid (the stacked hex+arith rows,
-		Width(dispW).
+	// where arith rows are already internally padded to hexW) into dispW.
-		Align(lipgloss.Center).
+	// We do this manually instead of lipgloss.NewStyle().Width(dispW).Align(Center).Render
-		Render(rawGrid)
+	// because the latter was producing inconsistent left padding on certain lines
+	// (especially bottom border lines containing box-drawing chars + heavy ANSI),
+	// causing the bottoms of the last row's keys to shift 1-2 columns relative to
+	// their own tops and sides.
+	kpLines := strings.Split(rawGrid, "\n")
+	for j := range kpLines {
+		cw := lipgloss.Width(kpLines[j])
+		if cw < dispW {
+			p := dispW - cw
+			l := p / 2
+			r := p - l
+			kpLines[j] = strings.Repeat(" ", l) + kpLines[j] + strings.Repeat(" ", r)
+		}
+	}
+	keypad := strings.Join(kpLines, "\n")
 
 	// Hint (minimal, non-wrapping, like gostations final player)
 	hint := lipgloss.NewStyle().Faint(true).Render("Tab:BASE  m:MOD  BackSpace:C  Del:AC")