feat: convert LunchTable to agent-only API-key and stream-audio pipeline

[Dexploarer]

Summary

• hard-cut active UX to agent-only control routes while preserving public spectator/watch overlays
• switched agent control surfaces to API-key-first auth flow (ltcg_ keys) with session bootstrap via query/postMessage/localStorage
• added per-agent authoritative stream audio control across Convex HTTP, overlay runtime, and plugin actions

Key Changes

• Added agent HTTP endpoints for lobby snapshot/chat, retake link/pipeline, and stream audio get/set
• Added streamAudioControls data model and convex/streamAudio.ts (agent + match resolution)
• Refactored agent lobby page to use API-key authenticated HTTP layer instead of user-bound flow
• Updated stream overlay hook/page to resolve agent control from matchId and apply remote playback/mute/volume state
• Added plugin client methods and new CONTROL_LTCG_STREAM_AUDIO action
• Enhanced stream pipeline to capture pulse audio when available and gracefully fallback to video-only with warning
• Removed AgentDev from product surface and converted /agent-dev to redirect-only
• Updated README/architecture docs for agent-only + API-key-first positioning

Verification

• bash scripts/pre-review-local.sh (APPROVE)
• bunx tsc --noEmit -p apps/web-tanstack/tsconfig.json
• bunx tsc --noEmit -p packages/plugin-ltcg/tsconfig.json
• bunx vitest run apps/web-tanstack/src/migrationParity.test.ts apps/web-tanstack/src/app/lib/agentOnlyRoutes.test.ts apps/web-tanstack/src/app/hooks/auth/useAgentApiSession.test.ts apps/web-tanstack/src/app/pages/StreamOverlay.test.ts apps/web-tanstack/src/app/pages/streamOverlay.audioMapping.test.ts packages/plugin-ltcg/src/__tests__/client.agent-controls.test.ts packages/plugin-ltcg/src/__tests__/control-stream-audio-action.test.ts packages/plugin-ltcg/src/__tests__/stream-pipeline.test.ts packages/plugin-ltcg/src/__tests__/retake.test.ts
• bunx vitest run --config convex/vitest.config.ts convex/__tests__/agentHttpRoutes.test.ts convex/__tests__/agentLobby.integration.test.ts convex/__tests__/streamAudio.integration.test.ts

Notes

• branch was rebased and pushed in review-fix-loop
• upstream remote now points to LunchTable-TCG/v2 (legacy remote still redirects)