Cli: headless 6502 frontend (assemble/run/disasm/hexdump)

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A command-line frontend for Learn6502 — the "fourth frontend" alongside the GNOME, web and Android apps. The key idea (per discussion): it is built on the same shared libraries rather than sitting underneath them — @learn6502/core (assembler + simulator) and @learn6502/common-ui (the DisplayWidget contract, createSimulatorStack, DEFAULT_COLOR_PALETTE). The GUIs remain library consumers; nothing depends on this CLI. It doubles as an executable proof that the core is genuinely UI-independent.

Commands

learn6502 assemble <file.asm>   Assemble and report the result
learn6502 run <file.asm>        Assemble, run, and render the display
learn6502 hexdump <file.asm>    Assemble and print a hexdump
learn6502 disasm <file.asm>     Assemble and print the disassembly

The display is just another platform

AnsiDisplay implements the same DisplayWidget interface the GTK (Gtk.DrawingArea+cairo), web (<canvas>) and Android displays implement. The 32×32 grid of memory $0200-$05FF prints as truecolor ANSI using the upper half-block ▀ (foreground = top pixel, background = bottom), so the screen stays roughly square in a terminal. run drives the simulator synchronously via debugExecStep() (with a step cap for programs that loop or await input) rather than the GUI's setInterval loop.

Verified

Built with gjsify build --app node (node-free-ready) and exercised end-to-end:

• assemble → "Code assembled successfully, 11 bytes."
• run on a colour-chart program → renders all 16 palette colours as vertical bands, "Program completed after 1026 steps."
• hexdump → 0600: a2 00 a5 fe 9d 00 02 e8 d0 f8 00
• disasm → full annotated disassembly table

The batch commands (assemble/disasm/hexdump) are thin wrappers over core; only run reaches for common-ui — an honest split between batch and interactive use. This is a spike: it validates the decoupling and the ANSI-display approach. Natural follow-ups: an interactive debug REPL (readline stepper over the existing debuggerController), stdin gamepad input, binary I/O (-o out.bin), and a --app gjs build.