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/FrameSampler.swift

@@ -92,9 +92,14 @@ struct FrameSampler {
         return points
     }
 
-    /// Grid-sampled pixel positions (top-left origin) that are strongly saturated
-    /// AND bright enough to be a UI highlight — i.e. a coloured speaking ring/border.
-    func saturatedPoints(threshold: Double = 0.5, minBrightness: Double = 60, gridStep: Int = 6) -> [CGPoint] {
+    /// Grid-sampled pixel positions (top-left origin) that are saturated AND bright
+    /// enough to be a UI highlight — i.e. a coloured speaking ring/border. `threshold`
+    /// is the minimum saturation; lower it for muted accent rings (Teams violet,
+    /// Meet's light-blue glow sit below the 0.5 default). `hueRange`, when set,
+    /// additionally restricts to a hue band (degrees, 0…360) so a low threshold
+    /// doesn't pick up warm video — the per-platform calibration lever.
+    func saturatedPoints(threshold: Double = 0.5, minBrightness: Double = 60,
+                         hueRange: ClosedRange<Double>? = nil, gridStep: Int = 6) -> [CGPoint] {
         var points: [CGPoint] = []
         var y = 0
         while y < height {
@@ -104,11 +109,26 @@ struct FrameSampler {
                 let r = Double(pixels[i]), g = Double(pixels[i + 1]), b = Double(pixels[i + 2])
                 let mx = max(r, g, b), mn = min(r, g, b)
                 let sat = mx > 0 ? (mx - mn) / mx : 0
-                if sat > threshold && mx > minBrightness { points.append(CGPoint(x: x, y: y)) }
+                if sat > threshold && mx > minBrightness,
+                   hueRange == nil || hueRange!.contains(Self.hueDegrees(r, g, b, mx, mn)) {
+                    points.append(CGPoint(x: x, y: y))
+                }
                 x += gridStep
             }
             y += gridStep
         }
         return points
     }
+
+    /// HSV hue in degrees (0…360) from RGB and its precomputed max/min channels.
+    private static func hueDegrees(_ r: Double, _ g: Double, _ b: Double, _ mx: Double, _ mn: Double) -> Double {
+        let d = mx - mn
+        guard d > 0 else { return 0 }
+        let h: Double
+        if mx == r { h = (g - b) / d }
+        else if mx == g { h = 2 + (b - r) / d }
+        else { h = 4 + (r - g) / d }
+        let deg = h * 60
+        return deg < 0 ? deg + 360 : deg
+    }
 }