chore(skeleton): minimal Go project layout + build system
- go.mod (1.24.2 + initial bubbletea/lipgloss)
- Makefile (build, install to ~/.local/bin/gralculator, test, clean; ldflags version injection)
- internal/version (ldflags-compatible String())
- main.go stub (version flag + placeholder)
- internal/calc/ (Engine skeleton with Base, CycleBase, IsInteger, ErrConversionNotPossible, FormatForDisplay stub + basic tests for CERR path)
- internal/ui/ (App model stub with Tab handling placeholder + lipgloss import for future rendering)
This establishes the three-phase foundation. Next: flesh out engine (phase 2), then TUI spike (phase 3). Paper trail continues.
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