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/Visual/GridCallAnalyzer.swift

@@ -27,6 +27,14 @@ struct GridCallAnalyzer {
         var nameAnchor: NameAnchor = .bottomCenter
         var detectColoredBorder = true
         var detectWhiteBorder = true
+        // Coloured-border sensitivity. Default 0.5 suits vivid rings (Zoom green/
+        // yellow); lower it for muted accent rings (Teams violet ≈ 0.41, Meet's
+        // light-blue glow ≈ 0.44). `colorHueRange` (degrees) optionally pins the
+        // ring's hue so a low threshold doesn't catch warm video — set per platform
+        // once calibrated against real screenshots.
+        var colorSaturation: Double = 0.5
+        var colorMinBrightness: Double = 60
+        var colorHueRange: ClosedRange<Double>? = nil
         var minTextConfidence: Float = 0.3
         var maxNameLength = 40
         var minHighlightPoints = 6
@@ -58,7 +66,11 @@ struct GridCallAnalyzer {
 
         // Highlight pixels: coloured (saturated) and/or white (thin near-white).
         var highlight: [CGPoint] = []
-        if config.detectColoredBorder { highlight += sampler.saturatedPoints() }
+        if config.detectColoredBorder {
+            highlight += sampler.saturatedPoints(threshold: config.colorSaturation,
+                                                 minBrightness: config.colorMinBrightness,
+                                                 hueRange: config.colorHueRange)
+        }
         if config.detectWhiteBorder { highlight += sampler.thinWhitePoints() }
 
         // Drop points inside any name-text region so the white name itself doesn't count.