fix(daemon): write PID and install signal handlers in foreground mode

[Maple-Aikon]

Linked issue

Closes a daemon lifecycle bug found while dogfooding crg-daemon start --foreground. No public issue number — happy to open one if maintainer prefers a tracked issue.

What & why

crg-daemon start --foreground leaks the PID file and ignores SIGTERM/SIGHUP. Cause: _handle_start short-circuits to daemonize() when is_daemon_running() is False. The non-daemonize (foreground) branch returns early without writing the PID file or installing signal handlers, so:

• crg-daemon stop fails with "PID file missing"
• The process cannot be terminated by signal
• crg watch / crg add workflows that need crg-daemon running in foreground become un-killable

The Windows branch of daemonize() already does write_pid() + self._setup_signal_handlers() — this PR applies the same pattern to the Linux/macOS foreground branch.

Diff

 def _handle_start(args: argparse.Namespace) -> None:
     """Start the daemon process."""
-    from .daemon import WatchDaemon, is_daemon_running, load_config
+    from .daemon import WatchDaemon, is_daemon_running, load_config, write_pid

     if is_daemon_running():
         print("Error: Daemon is already running.")

     if not args.foreground:
         daemon.daemonize()
+    else:
+        write_pid()
+        daemon._setup_signal_handlers()

     daemon.run_forever()

uv.lock was auto-updated by the cherry-pick (one transitive bump) — happy to drop it from the PR if maintainer prefers source-only diffs.

How it was tested

# Cherry-picked onto v2.3.6 base (b72413c)
$ uv run pytest tests/test_daemon.py -v --tb=short -q
============================== 51 passed in 0.29s ==============================

$ uvx ruff check code_review_graph/daemon_cli.py
All checks passed!

$ uvx mypy code_review_graph/daemon_cli.py --ignore-missing-imports --no-strict-optional
Success: no issues found in 1 source file

Manual functional test (with isolated HOME):

# Start foreground daemon
$ HOME=/tmp/crg-test/home uv run crg-daemon start --foreground &
# Process stays alive, PID file written:
$ cat /tmp/crg-test/home/.code-review-graph/daemon.pid
14469

# Send SIGTERM
$ kill -TERM 14466
# Daemon log shows graceful shutdown:
INFO: Received signal 15 — shutting down
INFO: Daemon stopped
# Process exits 0 within 5s

Before the fix: SIGTERM was ignored and the process had to be killed with SIGKILL.

Checklist

• Tests added for new functionality — N/A, this is a bug fix that brings the foreground branch in line with the Windows branch already covered by existing tests
• All tests pass: uv run pytest tests/test_daemon.py --tb=short -q → 51/51
• Linting passes: uvx ruff check code_review_graph/daemon_cli.py → clean
• Type checking passes: uvx mypy code_review_graph/daemon_cli.py --ignore-missing-imports --no-strict-optional → clean
• Lines are at most 100 characters
• Docs updated where behavior changed — happy to add a note to docs/CLI.md about foreground signal handling if maintainer wants