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/Adapters/TeamsAdapter.swift

@@ -0,0 +1,38 @@
+import Foundation
+import CoreVideo
+
+/// Microsoft Teams adapter (native app: com.microsoft.teams2 / .teams).
+///
+/// Teams' active-speaker cue is a **coloured ring/border** (Teams violet) around
+/// the speaking participant's tile; the **name sits in the tile's bottom-left**.
+/// Not a launch priority — included so the four detected platforms all have a
+/// visual adapter and degrade no worse than colored-border detection.
+///
+/// Detection *logic* is validated on synthetic frames; geometry constants are a
+/// first pass pending real Teams screenshots.
+struct TeamsAdapter: AppAdapter {
+    static let bundleIDs = ["com.microsoft.teams2", "com.microsoft.teams"]
+    let adapterVersion = "teams-0.1.0"
+    let preferredFPS = 3
+
+    private let analyzer: GridCallAnalyzer
+
+    init() {
+        var config = GridCallAnalyzer.Config()
+        config.nameAnchor = .bottomLeft
+        config.detectColoredBorder = true     // Teams-violet speaking ring
+        config.detectWhiteBorder = false
+        config.tileExpandX = 3.0
+        config.tileExpandY = 5.0
+        self.analyzer = GridCallAnalyzer(config: config)
+    }
+
+    func analyze(frame: CVPixelBuffer, at t: TimeInterval) -> [SpeakerObservation] {
+        analyzer.analyze(pixelBuffer: frame, at: t)
+    }
+
+    // Exposed for fixture/synthetic tests.
+    func analyze(cgImage: CGImage, at t: TimeInterval) -> [SpeakerObservation] {
+        analyzer.analyze(cgImage: cgImage, at: t)
+    }
+}