refactor: remove EXTERNAL_BROWSERLESS_WS / browserless fallback

- Delete infrastructure/browser/ directory entirely (browser pool is gone)
- Remove browser pool initialization from bootstrap
- Remove fetch_via_browserless fallback from proxy_fetch
- perform_proxy_chain now only uses relay endpoints
- Clean up log messages, README, and compose env var
The proxy-bun service at https://git.imrnes.team/MythEclipse/proxy-bun
handles all proxy needs now.

README.md

@@ -29,7 +29,6 @@ Optional yang sering dipakai:
 
 ```env
 RUST_LOG=info
-EXTERNAL_BROWSERLESS_WS=
 MINIO_ENDPOINT=
 MINIO_BUCKET_NAME=
 MINIO_ACCESS_KEY=