feat(simu): add opt-in Widget Studio automation hooks

[bultodepapas]

Summary of changes:

Adds an experimental, opt-in WIDGET_STUDIO mode to the native color-LCD simulator so visual Lua/LVGL tooling can drive the real EdgeTX runtime instead of maintaining a parallel renderer.

The option defaults to OFF and does not affect radio firmware, Companion embedding, or WASM builds.

What is included:

• an append-only --pipe <path> command-file interface for key, touch, capture, reset, reload, and exit commands
• deterministic one-shot PNG capture from the real RGB565 LCD framebuffer, including a forced LVGL redraw for static screens
• a simulator-only Lua simu table for named switch/analog input control, SD-mapped capture, and asynchronous reset
• synchronized shared state for firmware/Lua and SDL/UI threads
• documentation for the build option, command protocol, Lua API, capture behavior, and trust boundary

Implementation notes:

• WIDGET_STUDIO is defined only for the seven sources that implement the hooks.
• The stb PNG implementation is linked only into the interactive simu executable, avoiding duplicate stb symbols in gtests-radio and excluding it from WASM.
• The command reader tracks a monotonic offset, preserves partial lines, handles LF/CRLF and file shrink, and reads only the observed byte range so concurrent appends are not replayed.
• Host paths supplied through --pipe are intentionally treated as trusted local-development input. Lua capture paths are resolved through the configured SD-card mapping.

Validation performed on Windows with Ninja/MinGW, PCB=TX16SMK3, and Companion disabled:

• full WIDGET_STUDIO=OFF simu build passed; --help does not expose --pipe
• full WIDGET_STUDIO=ON simu build passed; --help exposes --pipe
• verified only seven object build rules receive WIDGET_STUDIO
• live headless run passed command-file truncation/resynchronization, incomplete-line buffering, paths containing spaces, reload, hot reset, repeated capture, invalid-key rejection, and clean exit (code 0)
• both generated PNGs had valid signatures and were visually inspected at the native 800x480 framebuffer size
• all 35 gtests-radio source objects compiled; the final local Windows link is blocked by the existing unconditional -fsanitize=address test flag because this MinGW installation has no libasan

This is intentionally a draft for maintainer feedback on the option/API shape and naming before treating it as a stable development interface.

This PR is independent of the Gauge Pro SD-card contribution (EdgeTX/edgetx-sdcard#289); the widgets do not depend on these hooks, although the hooks were used to exercise their visual catalog locally.

[bultodepapas]

CI status note: all documentation, test, and firmware-build jobs passed. Package firmwares successfully merged and uploaded all 19 artifacts, then failed during source-artifact cleanup with 404 Not Found: artifact does not exist. The contributor account does not have permission to rerun the upstream workflow.

@philmoz, could you provide early feedback on the opt-in option name, command protocol, and simulator-only Lua API while this remains a draft? If appropriate, could a maintainer also rerun the failed packaging job?

[pfeerick]

This looks like some overlap with #7337 at first glance? The build error seems to be a network outage issue, will probably resolve on the next commit.

[bultodepapas]

Thanks, @pfeerick. I agree that the overlap with #7337 is substantial and should be resolved before this draft grows further.

I opened #7668 as a collaborative consolidation draft. It uses #7337 as the generic harness foundation, carries forward the Windows, reset/reload, state-injection, and render-complete capture requirements explored here, and explicitly removes the duplicate or Widget Studio-specific surfaces.

I am not closing this PR yet. The new draft starts with the full contract, keep/drop matrix, phased implementation plan, tests, attribution policy, and rollback so @onliner10 and the simulator maintainers can shape the direction before implementation. The packaging failure is secondary until that direction is agreed.