fix: overlay rendering — vertical alignment, line artifact, and duplicate class members

Overlay renderer (xterm-zerolag-input):
- Add charTop/charHeight to CellDimensions and RenderParams for precise
  vertical text positioning matching xterm's canvas renderer
- Convert device.char dimensions to CSS pixels via devicePixelRatio
- Extend line div background 1px past cell boundary to cover compositing
  seam between overlay layer (z-index:7) and canvas layer below
- Remove -webkit-font-smoothing/text-rendering overrides that made overlay
  text thinner than canvas text
- Add per-span height/lineHeight for natural CSS vertical centering
- Add setPrompt() method for runtime prompt strategy switching (fixes tab
  switching crash with "setPrompt is not a function")

app.js duplicate class members:
- Remove dead formatTokens duplicate (line ~5590 shadowed precise version)
- Remove fire-and-forget resetCircuitBreaker duplicate (shadowed notification version)
- Rename mux-panel killAllSessions to killAllMuxSessions (was shadowing
  Codeman session killer, breaking Ctrl+K)

Other:
- Update index.html onclick to use killAllMuxSessions
- Add getTeamTasks mock to test route context

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

test/mocks/mock-route-context.ts

@@ -101,7 +101,7 @@ export function createMockRouteContext(options?: { sessionId?: string }) {
     runSummaryTrackers: new Map(),
     activePlanOrchestrators: new Map(),
     scheduledRuns: new Map(),
-    teamWatcher: { getTeams: vi.fn(() => []), hasActiveTeammates: vi.fn(() => false) },
+    teamWatcher: { getTeams: vi.fn(() => []), getTeamTasks: vi.fn(() => []), hasActiveTeammates: vi.fn(() => false) },
     tunnelManager: null,
     pushStore: null,
     startScheduledRun: vi.fn(),