f1-stream: only show streams confirmed playable by headless browser

Cuts the stream list from 23 mostly-broken entries to ~6 confirmed-playable
ones, and adds an iframe-stripping proxy so embed sources (hmembeds, etc.)
load through our origin without X-Frame-Options / CSP / JS frame-buster
blocks.

Why: the previous list was dominated by Discord-shared news article URLs,
hardcoded aggregator landing pages, and other non-stream URLs that all sat
at is_live=true because embed streams skipped the health check entirely.
Users could not tell which links would actually play.

What:
- backend/playback_verifier.py: new headless-Chromium verifier (Playwright)
  that polls each candidate stream for a codec-independent "playable" signal
  (hls.js MANIFEST_PARSED for m3u8; <video>/player div for embed). Replaces
  the unconditional is_live=True for embed streams in service.py.
- backend/embed_proxy.py: new /embed and /embed-asset routes that fetch
  upstream embed pages, strip X-Frame-Options/CSP/Set-Cookie, and inject a
  <base href> + frame-buster-defeat <script> that locks down window.top,
  document.referrer, console.clear/table, and window.location so the
  hmembeds disable-devtool.js redirect-to-google trap can't fire.
- extractors/curated.py: new always-on extractor with two known-good 24/7
  hmembeds embeds (Sky Sports F1, DAZN F1) so the list isn't empty between
  race weekends.
- extractors/__init__.py: register CuratedExtractor first; drop
  FallbackExtractor (its 10 aggregator landing-pages can't iframe-play).
- extractors/discord_source.py: positive-match path filter (must look like
  /embed/, /stream, /watch, /live, /player, *.m3u8, *.php) plus expanded
  domain blocklist for news sites — was 10 noise URLs, now ~1.
- extractors/service.py: run_extraction now health-checks AND verifier-
  checks both stream types; only verified-playable streams reach is_live.
- main.py: register /embed + /embed-asset routes; defer initial extraction
  by 8s so the verifier can reach the local /embed proxy on 127.0.0.1:8000.
- frontend/lib/api.js + watch/+page.svelte: route embed iframes through
  /embed proxy instead of the upstream URL, so X-Frame-Options/CSP can't
  block them.
- Dockerfile: install Playwright chromium + system codec-runtime libs.
- main.tf: bump pod memory 256Mi → 1Gi for chromium.

Verified end-to-end with Playwright against
https://f1.viktorbarzin.me/watch — 6/6 streams reach a player UI; the 3
demo m3u8s actually play (codec-bearing browser); the 3 embeds (Sky
Sports F1, DAZN F1, sportsurge) render iframes through the proxy.

Image: viktorbarzin/f1-stream:v6.0.5

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

stacks/f1-stream/files/Dockerfile

@@ -14,9 +14,26 @@ FROM python:3.13-slim-bookworm
 
 WORKDIR /app
 
+# Headless Chromium runtime libs for the playback verifier. Listed inline
+# (instead of running `playwright install-deps`) so the image build doesn't
+# need root-network apt fetches at runtime.
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    ca-certificates \
+    libnss3 libnspr4 \
+    libatk1.0-0 libatk-bridge2.0-0 libcups2 \
+    libdrm2 libxkbcommon0 libxcomposite1 libxdamage1 \
+    libxfixes3 libxrandr2 libgbm1 libpango-1.0-0 libcairo2 \
+    libasound2 libatspi2.0-0 \
+    fonts-liberation fonts-noto-color-emoji \
+ && rm -rf /var/lib/apt/lists/*
+
 COPY backend/requirements.txt .
 RUN pip install --no-cache-dir -r requirements.txt
 
+# Install the Chromium browser binary used by the verifier. Skip
+# --with-deps because we already installed the system libs above.
+RUN playwright install chromium
+
 COPY backend/ ./backend/
 
 # Copy built frontend into the image