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/ZoomAdapter.swift

@@ -0,0 +1,43 @@
+import Foundation
+import CoreVideo
+
+/// Zoom adapter (native app: us.zoom.xos).
+///
+/// Zoom's active-speaker cue is a **coloured border** around the speaking tile —
+/// by default a green/yellow outline (configurable in Zoom settings). The
+/// participant **name sits in the tile's bottom-LEFT corner**, so the tile is
+/// estimated extending up and to the right of the name.
+///
+/// Gotchas to calibrate against real fixtures later:
+/// - **Speaker view** shows one big tile; the active speaker fills it (no useful
+///   per-tile border) — handle by attributing speech to the large tile.
+/// - The self-view tile and screen-share change the layout.
+///
+/// Detection *logic* is validated on synthetic frames; geometry constants are a
+/// first pass pending real Zoom screenshots.
+struct ZoomAdapter: AppAdapter {
+    static let bundleIDs = ["us.zoom.xos"]
+    let adapterVersion = "zoom-0.1.0"
+    let preferredFPS = 3
+
+    private let analyzer: GridCallAnalyzer
+
+    init() {
+        var config = GridCallAnalyzer.Config()
+        config.nameAnchor = .bottomLeft
+        config.detectColoredBorder = true     // green/yellow speaking border
+        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)
+    }
+}