fix(crawler): wrap wait_for_navigation in 30s timeout (0.36.1)

A hung TLS handshake or a page that never fires load could wedge a
worker (or the cron metadata pass) indefinitely — chromiumoxide
imposes no navigation timeout of its own.

New crawler::nav::wait_for_nav caps each navigation at NAV_TIMEOUT
(30s) and returns a typed NavError so timeouts surface as transient
(retryable) errors. Wired at the three navigation sites:
- source::target::navigate (catalog/detail/pagination)
- content::sync_chapter_content (chapter reader)
- session::fetch_probe_html (session probe)

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

backend/Cargo.lock

@@ -1470,7 +1470,7 @@ checksum = "c41e0c4fef86961ac6d6f8a82609f55f31b05e4fce149ac5710e439df7619ba4"
 
 [[package]]
 name = "mangalord"
-version = "0.36.0"
+version = "0.36.1"
 dependencies = [
  "anyhow",
  "argon2",