feat(scraper): harden browser headers and add proxy support

Upgrade DirectHTTPClient to send a full Chrome 124 header set
(Sec-Fetch-*, Accept-Encoding with gzip decompression, Referer,
Cache-Control) to reduce bot-detection false positives on WAFs.

Add SCRAPER_PROXY env var to route all outbound scrape requests
through a configurable proxy (residential or otherwise); falls back
to the standard HTTP_PROXY / HTTPS_PROXY env vars.

scraper/cmd/scraper/main.go

@@ -12,6 +12,10 @@
 //
 //	SCRAPER_WORKERS             Chapter goroutine count        (default: NumCPU)
 //	SCRAPER_HTTP_ADDR           HTTP listen address            (default: :8080)
+//	SCRAPER_PROXY               Outbound proxy for all scraper requests, e.g.
+//	                            http://user:pass@proxy-host:3128 — use a
+//	                            residential proxy to bypass datacenter IP blocks.
+//	                            Falls back to HTTP_PROXY / HTTPS_PROXY if unset.
 //	KOKORO_URL                  Kokoro-FastAPI base URL        (default: "")
 //	KOKORO_VOICE                Default TTS voice              (default: af_bella)
 //	POCKETBASE_URL              PocketBase API base URL        (default: http://localhost:8090)
@@ -493,6 +497,7 @@ Environment variables:
   SCRAPER_WORKERS             Chapter goroutines        (default: NumCPU = %d)
   SCRAPER_HTTP_ADDR           HTTP listen address       (default: :8080)
   SCRAPER_TIMEOUT             HTTP request timeout sec  (default: 90)
+  SCRAPER_PROXY               Outbound proxy URL        (default: "", falls back to HTTP_PROXY/HTTPS_PROXY)
   KOKORO_URL                  Kokoro-FastAPI base URL   (default: "", TTS disabled)
   KOKORO_VOICE                Default TTS voice         (default: af_bella)
   POCKETBASE_URL              PocketBase base URL       (default: http://localhost:8090)