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.

README.md

@@ -187,7 +187,8 @@ frontend/
 Everything needed to deploy and configure the stack (Docker, Nginx, Cloudflare rules, future Terraform).
 
 - Cloudflare
-  - [worker.js](infrastructure/cloudflare/worker.js) — Cloudflare Worker serving the static SPA and adding immutable cache headers to HLS segments
+  - [linearvoid-media worker](infrastructure/cloudflare/) — R2-bound edge Worker serving HLS on `media.linearvoid.tv` (immutable segment caching, CORS, Range)
+  - [linearvoid-frontend worker](frontend/wrangler.toml) — serves the static SPA on `linearvoid.tv`
 - Nginx
   - [Dockerfile](infrastructure/nginx/Dockerfile) — builds Nginx with custom config
   - [nginx.conf](infrastructure/nginx/nginx.conf) — reverse proxy, static SPA, HLS delivery