Add comprehensive documentation for Linear Void project

- Created README.md in docs folder outlining project structure and documentation links.
- Added SECURITY.md detailing the security model, threat model, authentication, transport security, network isolation, and incident response procedures.
- Introduced SETUP.md providing a detailed setup guide for local and production environments, including prerequisites, environment setup, and Gitea integration.
- Added STREAMING.md outlining the streaming pipeline, including production flow, source-media contract, playout and HLS packaging, cache contract, player behavior, and monitoring.
- Updated architecture documentation to include links to new SETUP.md and STREAMING.md files for better navigation.

docs/DEVELOPMENT.md

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+# DEVELOPMENT.md — Linear Void Remaining Tasks
+
+## Test Fixtures (BLOCKED — requires ffmpeg)
+
+- [ ] Create test media fixtures in `backend/playout/testdata/`:
+  - `valid_720p30.mp4` — small (1-2s) H.264/AAC compliant file
+  - `invalid_h265.mp4` — wrong codec
+  - `invalid_24fps.mp4` — wrong framerate
+  - Generate via `ffmpeg` commands documented in test file headers
+
+- [ ] Create test playlist fixtures in `backend/playout/testdata/`:
+  - `valid_playlist.txt`, `empty_playlist.txt`, `comments_only.txt`, `mixed_valid_invalid.txt`
+
+## User Frontend Tests
+
+- [ ] Video player behavior (play, pause, seek, buffering, error handling)
+- [ ] Chat functionality (send/receive messages, presence, rate limiting, moderation)
+- [ ] State management and data flow
+- [ ] Responsive design and layout across different screen sizes
+- [ ] Accessibility testing (keyboard navigation, screen reader support)
+- [ ] Integration with backend APIs (mocking API responses for testing)
+- [ ] Test coverage for all critical frontend components and interactions
+- [ ] Add code coverage reporting and enforce minimum coverage threshold in CI/CD pipeline
+- [ ] Document test cases and expected outcomes
+
+## Admin Frontend Tests
+
+- [ ] Playlist management UI (add/remove videos, reorder, normalize)
+- [ ] User moderation tools (mute/ban/report users, view moderation logs)
+- [ ] Metrics and monitoring dashboards (Prometheus/Grafana integration)
+- [ ] State management and data flow
+- [ ] Responsive design and layout across different screen sizes
+- [ ] Accessibility testing (keyboard navigation, screen reader support)
+- [ ] Integration with backend APIs (mocking API responses for testing)
+- [ ] Test coverage for all critical admin UI components and interactions
+- [ ] Add code coverage reporting and enforce minimum coverage threshold in CI/CD pipeline
+- [ ] Document test cases and expected outcomes
+
+## Cloudflare R2 Integration Test
+
+- [ ] Upload test HLS segments and manifests to R2 bucket
+- [ ] Verify correct cache headers are applied (immutable segments, TTLs)
+- [ ] Test retrieval of segments and manifests from R2 via Cloudflare edge
+- [ ] Validate cache hit/miss behavior and performance metrics
+- [ ] Ensure integration test can run in CI/CD pipeline with proper mocking/stubbing of R2 API
+- [ ] Document test cases and expected outcomes
+
+## Cloudflare Configuration (manual — Cloudflare dashboard)
+
+> Evidence tracker: `docs/operations/cloudflare-uptimerobot-checklist.md`
+
+- [ ] Cloudflare Pages: link Gitea repo, build `cd frontend && npm run build`, output `frontend/dist`
+- [ ] Tiered Cache: enable Smart Tiered Cache, validate `Cf-Cache-Status: HIT` from upper tier
+- [ ] WAF: enable OWASP Managed Ruleset, set to Simulate → review 48h → Block, enable Bot Fight Mode
+- [ ] Rate limiting: `/api/admin/login` + `/api/admin/*` → 10 req/10s per IP, Challenge action
+- [ ] HTTPS/WSS: Always Use HTTPS, HSTS max-age=31536000 includeSubDomains preload, min TLS 1.2
+- [ ] HTTPS/WSS: enforce at edge (Cloudflare) and origin (nginx), redirect HTTP → HTTPS
+
+## External Services
+
+> Evidence tracker: `docs/operations/cloudflare-uptimerobot-checklist.md`
+
+- [ ] UptimeRobot: add HTTP monitor for `https://linearvoid.tv/health` (5min interval)
+- [ ] UptimeRobot: add keyword monitor for `https://linearvoid.tv/hls/playlist.m3u8` (keyword: `#EXTM3U`, 5min)
+- [ ] Alert on 2 consecutive failures, notify via email + Discord/Slack webhook
+
+## Production Deployment (Hetzner — not provisioned)
+
+- [ ] Provision Hetzner CX22 (2 vCPU, 4 GB, 40 GB) in Ashburn VA, Ubuntu 24.04
+- [ ] Install Docker Engine + Compose plugin, open firewall: 80/443 (public), 2375 (runner IP only)
+- [ ] Configure Docker daemon for remote TLS access (`-H tcp://0.0.0.0:2376` with certs)
+- [ ] Create `/srv/linearvoid/data/{playlist,media,hls,chat,slate}` directories
+- [ ] Add `CI_PROD_*` secrets to Gitea: DOCKER_HOST, R2 keys, admin password, DB password, Grafana password
+- [ ] Trigger CD workflow with `DOCKER_HOST` pointing to Hetzner IP
+- [ ] Verify all 11 containers start healthy, check `/health`, `/hls/playlist.m3u8`, WebSocket
+- [ ] Update Cloudflare A record `linearvoid.tv` → Hetzner IP, SSL Full (strict), test HTTPS + WSS
+- [ ] Smoke test: viewer SPA loads, HLS plays, chat connects, admin login → upload → playlist → playout
+- [ ] Set up Prometheus alerting notifications + UptimeRobot on production URL
+- [ ] Run `scripts/backup-db.sh` + `scripts/verify-backups.sh` on production host
+- [ ] Document production IP, SSH access, rollback procedure, scaling thresholds
+
+## Scaling & Performance (planning only)
+
+- [ ] Tune manifest TTL: measure `Cf-Cache-Status` distribution, adjust to 0.5× segment duration
+- [ ] Measure TTFB: WebPageTest from 3+ US regions, target <4s warm cache, document baseline
+- [ ] Load-test WebSocket: `artillery` or Go script, ramp 10→100→500→1000 connections, measure p95 latency + errors
+- [ ] Benchmark admin API: `wrk`/`k6` against `/api/admin/*`, target p95 <1s, identify slow queries
+- [ ] Track cache hit ratio: Cloudflare GraphQL → Grafana panel, alert <90%
+- [ ] Capacity triggers: Prometheus rules for cache-miss >10%/15min, chat p95 >1s/5min, CPU >80%/10min
+- [ ] Phase 2 plan: document boundaries (playout CPU, chat latency, DB state, monitoring), estimate per-service resources
+- [ ] Phase 3 plan: research second Hetzner location, design warm standby + DNS failover + DB/Redis replication