fix(visaged): handle SIGTERM (closes #26)

[ccross2]

Summary

Closes #26 — systemctl restart visaged.service hangs for ~90s after hibernate resume because visaged ignores SIGTERM.

Root cause

crates/visaged/src/main.rs:91 used tokio::signal::ctrl_c().await? for shutdown. On Unix, tokio::signal::ctrl_c() is SIGINT-only. systemd's systemctl stop / systemctl restart sends SIGTERM, which the daemon has no handler for — so systemd waits the default TimeoutStopSec=90s before escalating to SIGKILL. Reported as the ~90s window during which face auth doesn't work after visage-resume.service fires.

Note: this is independent of the stale-camera-fd concern in the original report. The fd may indeed go bad across hibernate, but the user-visible 90s hang is entirely on the signal-handling side — we never reach any shutdown / fd-teardown path.

Fix

Two changes:

1. crates/visaged/src/main.rs — install handlers for both SIGINT and SIGTERM via tokio::signal::unix::signal(SignalKind::terminate()) + SignalKind::interrupt(), awaited in a tokio::select!. Matches the pattern used in our other daemons (e.g. esver-capture-cli's wait_for_shutdown_signal).
2. packaging/systemd/visaged.service — add TimeoutStopSec=10s as defense in depth, in case a v4l2 capture is mid-flight and not promptly interruptible (e.g. a stale camera fd on hibernate resume that the v4l ioctl can't immediately abort).

Verification

• Mechanical correctness: the engine task is parked on rx.blocking_recv() (crates/visaged/src/engine.rs:166); when main returns and the tokio runtime drops, the channel sender drops, the engine thread exits cleanly. No new shutdown plumbing required.
• Worst-case systemctl restart goes from ~90s → ~10s for the rare case where the capture loop genuinely can't unwind in time.
• Local cargo check blocked on a devshell gap (missing libclang for v4l2-sys bindgen, missing rustfmt/clippy) — CI will run all gates. I'll file a separate PR to round out the devshell.

Test plan

• CI: cargo fmt --all -- --check clean
• CI: cargo clippy --workspace -- -D warnings clean
• CI: cargo test --workspace green
• CI: build-deb produces a .deb cleanly
• Manual on a hibernate-capable system (Surface / ThinkPad pre-Gen11 / EliteBook / Zenbook 14):
  • sudo systemctl restart visaged.service returns in ~1s when idle (was ~1s before, should still be ~1s — sanity check)
  • sudo systemctl restart visaged.service returns in ≤10s after hibernate resume (previously ~90s)
  • Face auth resumes working without further intervention

CHANGELOG

Entry added under [Unreleased] > Fixed. Will land in v0.3.2 per the release plan.

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