Add TX16S UI harness

[onliner10]

Fixes: N/A

Summary of Changes

This adds a repeatable TX16S UI automation harness for simulator-driven UI work.

The goal is to make future color LCD/touch UI changes easier to review, easier to automate, and safer to regression-test before touching production UI code.

Why This Is Being Added

EdgeTX UI work currently depends heavily on manually launching the simulator, navigating screens by hand, and capturing host-window screenshots. That makes visual regression checks hard to repeat and easy to skew by local window scale, focus, or setup state.

This harness provides a small, opt-in control plane around the existing simulator so contributors can build, navigate, and capture framebuffer screenshots in a reproducible way.

It also makes EdgeTX much easier to work on with AI coding agents. The simulator can be exposed as an MCP server, so an agent can start a TX16S simulator session, press keys, rotate, tap, wait, capture screenshots, and inspect UI state without relying on manual host-window interaction. That should make UI work more reviewable and less speculative.

This is intended as groundwork for future TX16S-class color touchscreen UI improvements. It does not redesign the UI and does not change model storage, EEPROM format, Lua APIs, or normal simulator behavior.

What Changed

• Adds --automation-stdio to the SDL simulator as an opt-in automation mode.
• Exposes simple simulator commands for status, key press, long press, rotary, touch, wait, screenshot, and stop.
• Captures screenshots from the simulator framebuffer through simuLcdCopy, avoiding host-window screenshots.
• Adds tools/ui-harness/edgetx-ui CLI for build, smoke, and JSON flow execution.
• Adds tools/ui-harness/edgetx-mcp as a stdio MCP wrapper using the same Python core as the CLI.
• Adds a TX16S smoke flow that captures home, menu, and return-home screenshots.
• Adds minimal TX16S settings fixtures for deterministic simulator startup.
• Adds uv project metadata so contributors can run the harness with a known Python dependency set.
• Adds EDGE_TX_BUILD_TESTS so this harness build path can avoid fetching/building native tests when they are not needed.

Contribution / Review Notes

• This PR is a tooling contribution intended to make simulator UI testing repeatable.
• The simulator automation mode is opt-in and only active when --automation-stdio is passed.
• Normal SDL simulator usage should remain unchanged.
• Native tests still default to enabled. The new EDGE_TX_BUILD_TESTS option only disables them when explicitly set to OFF.
• The first target is TX16S (PCB=X10, PCBREV=TX16S), but the harness is structured so more color LCD/touch targets can be added later.

Verification

uv run tools/ui-harness/edgetx-ui build tx16s
uv run tools/ui-harness/edgetx-ui run-flow tools/ui-harness/flows/tx16s-smoke.json
uv run python -m compileall tools/ui-harness/edgetx_ui

The smoke flow produced three valid 480x272 PNG screenshots from the simulator framebuffer:

• home
• menu
• return-home