feat(cloudflare): add linearvoid-media edge worker for R2 HLS delivery

Replace the ad-hoc `worker.js` with a self-contained `linearvoid-media`
worker under `infrastructure/cloudflare/` that owns `media.linearvoid.tv`.
It serves HLS objects from the R2 bucket, enforcing immutable Cache-Control
on segments, a short TTL on live manifests, plus HLS CORS, OPTIONS
preflight, Range support, and a `/health` probe. Includes wrapper config
with production domain, Vitest unit tests, Miniflare R2 integration tests,
automated deploy workflow, and docs updates.

infrastructure/cloudflare/.gitignore

@@ -0,0 +1,5 @@
+node_modules/
+.wrangler/
+dist/
+coverage/
+*.log