fix(daemons): race in-flight work against cancellation on shutdown (0.87.4)

Two high findings sharing one root cause: long-running daemon work that
ignored the shutdown signal until it finished naturally.

**Cron tick (crawler).** `CronContext::run_tick` ran the metadata-pass
body inside `AssertUnwindSafe(...).catch_unwind().await` with no
cancellation. A fresh-catalog walk (many minutes) wedged
`DaemonHandle::shutdown`, `Supervisors::reload_crawler` (under the
supervisor lock), and SIGTERM responsiveness for the whole pass.

Wrap the body in `tokio::select! { biased; _ = self.cancel.cancelled() => ...; r = body => ... }`.
On cancel the body future drops, which cascades to dropping
`metadata.run()` — exactly what gives Chromium/lease teardown a chance
via the BrowserManager idle reaper. The advisory unlock + conn drop
still run unconditionally.

**Analysis dispatch.** `process_lease` wrapped the vision call only in
`tokio::time::timeout(self.job_timeout, …)` — default 600s. Toggling
analysis off in the dashboard (under the supervisor lock) or stopping
the container blocked on whichever call was in flight. Same fix:
`tokio::select!` against `self.cancel.cancelled()`. On cancel,
`jobs::release` returns the lease to the queue without burning an
attempt — next tick picks it up.

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

backend/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "mangalord"
-version = "0.87.3"
+version = "0.87.4"
 edition = "2021"
 default-run = "mangalord"