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/content.rs

@@ -91,6 +91,7 @@ pub async fn sync_chapter_content(
     force_refetch: bool,
     allowlist: &DownloadAllowlist,
     max_image_bytes: usize,
+    _tor: Option<&crate::crawler::tor::TorController>,
 ) -> anyhow::Result<SyncOutcome> {
     // Skip if already fetched, unless caller explicitly forces.
     if !force_refetch {