Per-platform colour-border sensitivity (Teams violet, Meet glow)

Cross-platform research (Grant) flagged that the colour-border cue differs by app;
checking the real brand colours against the detector found a concrete bug: the
global 0.5 saturation threshold MISSES Teams' violet ring (#6264A7 ≈ 0.41, light
variants ~0.27) entirely and Meet's lighter blue glow (#8ab4f8 ≈ 0.44). Those
adapters would have detected nothing.

- FrameSampler.saturatedPoints: add a tunable threshold + optional hue-band gate
  (degrees) so a lowered threshold doesn't pick up warm video.
- GridCallAnalyzer.Config: colorSaturation / colorMinBrightness / colorHueRange,
  plumbed to the colour-border path (defaults preserve prior behaviour).
- MeetAdapter sat→0.35 (catch the glow); TeamsAdapter sat→0.22 + hue 215–275°
  (catch the faint violet, reject other colours); ZoomAdapter sat 0.45 + hue
  40–150° (vivid green/yellow). Values are first-pass pending real-fixture
  calibration; the hue gate is the main calibration lever.

Tests: Teams now detects the faint violet ring and rejects a green one; Meet/Zoom
vivid cases still pass. 27/27 XCTest.

Ten31Transcripts/Adapters/MeetAdapter.swift

@@ -27,8 +27,11 @@ struct MeetAdapter: AppAdapter {
     init() {
         var config = GridCallAnalyzer.Config()
         config.nameAnchor = .bottomLeft
-        config.detectColoredBorder = true     // Google-blue speaking ring
+        config.detectColoredBorder = true     // Google-blue speaking ring/glow
         config.detectWhiteBorder = false
+        // The bright ring (#1a73e8) is ~0.89 sat but the lighter glow (#8ab4f8) is
+        // ~0.44, below the 0.5 default — lower the threshold so the glow registers.
+        config.colorSaturation = 0.35
         config.tileExpandX = 3.0
         config.tileExpandY = 5.0
         self.analyzer = GridCallAnalyzer(config: config)