feat(crawler): plumb TorController through FetchContext and pipelines

Adds CRAWLER_TOR_CONTROL_URL / _PASSWORD / _COOKIE_PATH /
_RECIRCUIT_MAX_ATTEMPTS to CrawlerConfig and to bin/crawler.rs's
env reads. Constructs an Option<Arc<TorController>> at daemon /
CLI startup and threads it through FetchContext,
pipeline::run_metadata_pass, and content::sync_chapter_content as
Option<&TorController>.

Pure scaffolding — the controller isn't used yet; behavior is
unchanged. Next commit wires the retry hooks and session-probe
recircuit.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/src/crawler/pipeline.rs

@@ -103,6 +103,7 @@ pub async fn run_metadata_pass(
     skip_chapters: bool,
     allowlist: &DownloadAllowlist,
     max_image_bytes: usize,
+    tor: Option<&crate::crawler::tor::TorController>,
 ) -> anyhow::Result<MetadataStats> {
     let lease = browser_manager
         .acquire()
@@ -121,6 +122,7 @@ pub async fn run_metadata_pass(
     let ctx = FetchContext {
         browser: browser_ref,
         rate,
+        tor,
     };
 
     let source_id = source.id();