Add wait-for-region-colour (appear/vanish)

[JE-Chen]

Summary

Round-11, automation-core. wait_for_pixel matches one point exactly and wait_until_pixel_changes detects any change at one point — neither waits for "the status light turns green" / "the progress bar fills" / "the red banner is gone".

Layers

• Headless core: extends smart_waits/waits.py — wait_until_color (counts pixels within tolerance of target_rgb over a region; succeeds when the fraction crosses min_fraction, or drops below it for present=False) + pure _color_fraction helper. Injectable sampler. Returns the existing WaitOutcome.
• Facade: wait_until_color re-exported + __all__.
• Executor: AC_wait_color (JSON target_rgb/region).
• MCP: ac_wait_color.
• Script Builder: one CommandSpec under Flow.

Tests / docs

• test/unit_test/headless/test_wait_color_batch.py — 8 headless tests (reaches fraction, timeout, vanish, tolerance band, validation, pure fraction helper + wiring + facade) via injected sampler.
• EN/Zh feature docs v121_features_doc.rst + toctrees; 3 WHATS_NEW entries.

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[codacy-production]

Not up to standards ⛔

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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