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.

src/infrastructure/repository/alqanime.rs

@@ -94,7 +94,7 @@ impl ScrapingRepository for AlqanimeRepository {
             .await
             .map_err(|e| ScrapingError::Http(format!("Alqanime fetch failed: {}", e)))?;
         if response.data.trim().is_empty() {
-            warn!("Alqanime browserless fetch returned empty body for {}", url);
+            warn!("Alqanime fetch returned empty body for {}", url);
         }
         Ok(response.data)
     }