Adapters: add Meet, Zoom, Teams (coloured border) + adapter registry

Front-loads the remaining visual adapters per the Signal→Meet→Zoom priority.
All three reuse GridCallAnalyzer's coloured-border (saturated) detection path
and share the new bottom-left name anchor:

- GridCallAnalyzer: generalise nameAtBottom:Bool into a NameAnchor enum
  (.bottomCenter for Signal's centered footer, .bottomLeft for Meet/Zoom/Teams
  where the name hugs the tile's bottom-left corner, .center for completeness).
  tileRect estimates the tile up-and-right of a bottom-left name.
- MeetAdapter (Google-blue ring, browser-hosted), ZoomAdapter (green/yellow
  border), TeamsAdapter (violet ring): coloured-border on, white-border off,
  bottom-left names. Geometry constants are first-pass pending real fixtures.
- AdapterRegistry.adapter(for:) maps CallDetector.DetectedApp → AppAdapter so
  VisualObserver can be constructed when live visual capture is wired in;
  unmapped apps degrade to audio-only.

Synthetic 4-tile tests: Meet picks each blue-bordered speaker with no
adjacent-tile bleed, Zoom picks the green-bordered speaker, and Signal's
white-only detector correctly ignores a coloured border. 18/18 XCTest pass.

Ten31Transcripts/Visual/GridCallAnalyzer.swift

@@ -13,10 +13,18 @@ import CoreImage
 /// Geometry (`Config`) is a first pass; tile expansion calibrates per app against
 /// real screenshot fixtures. Detection *logic* is validated on synthetic frames.
 struct GridCallAnalyzer {
+    /// Where the name label sits relative to its participant tile — drives how the
+    /// tile rect is estimated from the OCR'd name box.
+    enum NameAnchor {
+        case bottomCenter   // Signal: centered footer; tile extends UP, centered on the name
+        case bottomLeft     // Meet/Zoom: name in the bottom-left corner; tile extends UP and RIGHT
+        case center         // name centered inside the tile
+    }
+
     struct Config {
         var tileExpandX = 2.4         // tile width  ≈ name width  × this
         var tileExpandY = 4.8         // tile height ≈ name height × this
-        var nameAtBottom = true       // Signal/most: name footer sits at the tile bottom
+        var nameAnchor: NameAnchor = .bottomCenter
         var detectColoredBorder = true
         var detectWhiteBorder = true
         var minTextConfidence: Float = 0.3
@@ -91,20 +99,27 @@ struct GridCallAnalyzer {
         return CGRect(x: box.minX * W, y: (1 - box.maxY) * H, width: box.width * W, height: box.height * H)
     }
 
-    /// Estimate the participant tile from the name label. With `nameAtBottom`, the
-    /// tile extends UP from the footer (Signal); otherwise it's centred on the name.
+    /// Estimate the participant tile from the name label, per the app's `nameAnchor`:
+    /// - `.bottomCenter` (Signal): tile extends UP from a centered footer.
+    /// - `.bottomLeft` (Meet/Zoom): name hugs the tile's bottom-left corner; the
+    ///   tile extends UP and to the RIGHT of it.
+    /// - `.center`: tile centered on the name.
     private func tileRect(_ box: CGRect, _ w: Int, _ h: Int) -> CGRect {
         let W = Double(w), H = Double(h)
         let name = pixelRect(box, w, h)
         let nw = name.width * config.tileExpandX
         let nh = name.height * config.tileExpandY
-        let cx = name.midX
         let rect: CGRect
-        if config.nameAtBottom {
+        switch config.nameAnchor {
+        case .bottomCenter:
             let bottom = name.maxY + name.height * 0.3
-            rect = CGRect(x: cx - nw / 2, y: bottom - nh, width: nw, height: nh)
-        } else {
-            rect = CGRect(x: cx - nw / 2, y: name.midY - nh / 2, width: nw, height: nh)
+            rect = CGRect(x: name.midX - nw / 2, y: bottom - nh, width: nw, height: nh)
+        case .bottomLeft:
+            let bottom = name.maxY + name.height * 0.3
+            let left = name.minX - name.height * 0.4   // small left padding ≈ the corner gutter
+            rect = CGRect(x: left, y: bottom - nh, width: nw, height: nh)
+        case .center:
+            rect = CGRect(x: name.midX - nw / 2, y: name.midY - nh / 2, width: nw, height: nh)
         }
         return rect.intersection(CGRect(x: 0, y: 0, width: W, height: H))
     }