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.

Ten31TranscriptsTests/GridCallAnalyzerTests.swift

@@ -61,4 +61,67 @@ final class GridCallAnalyzerTests: XCTestCase {
         XCTAssertEqual(speaking.first?.bbox.midX ?? 0, 210, accuracy: 160)
         XCTAssertEqual(speaking.first?.bbox.midY ?? 0, 435, accuracy: 160)
     }
+
+    // MARK: - Coloured-border apps (Meet / Zoom / Teams): name in bottom-LEFT corner.
+
+    private func leftText(_ s: String, _ ctx: CGContext, leftBaseline: CGPoint, size: CGFloat) {
+        let font = CTFontCreateWithName("Helvetica-Bold" as CFString, size, nil)
+        let attrs = [kCTFontAttributeName: font,
+                     kCTForegroundColorAttributeName: CGColor(red: 1, green: 1, blue: 1, alpha: 1)] as CFDictionary
+        let line = CTLineCreateWithAttributedString(CFAttributedStringCreate(nil, s as CFString, attrs)!)
+        ctx.textPosition = leftBaseline
+        CTLineDraw(line, ctx)
+    }
+
+    private func coloredFrame(speakingIndex: Int, border: CGColor) -> CGImage {
+        let W = 900, H = 640
+        let ctx = CGContext(data: nil, width: W, height: H, bitsPerComponent: 8, bytesPerRow: 0,
+                            space: CGColorSpaceCreateDeviceRGB(),
+                            bitmapInfo: CGImageAlphaInfo.premultipliedLast.rawValue)!
+        ctx.setFillColor(CGColor(red: 0.1, green: 0.1, blue: 0.12, alpha: 1))
+        ctx.fill(CGRect(x: 0, y: 0, width: W, height: H))
+        let rects: [(String, CGRect)] = [
+            ("GRANT", CGRect(x: 40, y: 340, width: 380, height: 250)),
+            ("SARAH", CGRect(x: 480, y: 340, width: 380, height: 250)),
+            ("DMITRI", CGRect(x: 40, y: 50, width: 380, height: 250)),
+            ("ALEX", CGRect(x: 480, y: 50, width: 380, height: 250)),
+        ]
+        for (i, (name, rect)) in rects.enumerated() {
+            ctx.setFillColor(CGColor(red: 0.18, green: 0.18, blue: 0.2, alpha: 1)); ctx.fill(rect)
+            if i == speakingIndex {
+                ctx.setStrokeColor(border); ctx.setLineWidth(8)
+                ctx.stroke(rect.insetBy(dx: 4, dy: 4))
+            }
+            // Name in the bottom-LEFT corner (bottom-left origin: near minX/minY).
+            leftText(name, ctx, leftBaseline: CGPoint(x: rect.minX + 16, y: rect.minY + 16), size: 40)
+        }
+        return ctx.makeImage()!
+    }
+
+    func testMeetPicksBlueBorderedSpeaker() {
+        let blue = CGColor(red: 0.16, green: 0.45, blue: 0.95, alpha: 1)
+        for (idx, name) in ["GRANT", "SARAH", "DMITRI", "ALEX"].enumerated() {
+            let obs = MeetAdapter().analyze(cgImage: coloredFrame(speakingIndex: idx, border: blue), at: 0)
+            let speaking = Set(obs.filter { $0.speaking }.map { $0.name })
+            XCTAssertEqual(speaking, [name], "Meet: only \(name) should be speaking")
+        }
+        // No border → no speaker.
+        let none = MeetAdapter().analyze(cgImage: coloredFrame(speakingIndex: -1, border: blue), at: 0)
+        XCTAssertTrue(none.filter { $0.speaking }.isEmpty)
+    }
+
+    func testZoomPicksGreenBorderedSpeaker() {
+        let green = CGColor(red: 0.2, green: 0.85, blue: 0.3, alpha: 1)
+        let obs = ZoomAdapter().analyze(cgImage: coloredFrame(speakingIndex: 3, border: green), at: 0)   // ALEX
+        let speaking = Set(obs.filter { $0.speaking }.map { $0.name })
+        XCTAssertEqual(speaking, ["ALEX"])
+    }
+
+    func testWhiteBorderDetectorIgnoresColouredBorder() {
+        // Signal looks only for the white border, so a coloured (Meet) border must
+        // not register as a Signal speaker.
+        let blue = CGColor(red: 0.16, green: 0.45, blue: 0.95, alpha: 1)
+        let obs = SignalAdapter().analyze(cgImage: coloredFrame(speakingIndex: 0, border: blue), at: 0)
+        XCTAssertTrue(obs.filter { $0.speaking }.isEmpty)
+    }
 }