feat(cli): codegraph stop / list to manage background daemons (#861)

Adds first-class daemon control (the #845 pain point: no clean way to stop a
runaway daemon). `codegraph stop [path]` stops the current/given project's
daemon (SIGTERM -> SIGKILL fallback, sweeps artifacts); `stop --all` stops every
daemon; `list`/`ps` shows running daemons (--json for scripts).

Discovery via a small self-healing registry: each daemon records its root under
~/.codegraph/daemons/ on start, removes it on graceful shutdown; readers prune
dead pids. Cross-platform by construction (files + process.kill). Validated live
on macOS, Linux (docker), and Windows (VM): registry unit 6/6 and real-daemon
stop/list 6/6 on each.

CHANGELOG.md

@@ -11,6 +11,7 @@ and adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ### New Features
 
+- New `codegraph list` and `codegraph stop` commands for managing the background daemon. `codegraph list` (alias `ps`) shows every running CodeGraph daemon — project, pid, version, uptime — with `--json` for scripting. `codegraph stop` stops the daemon for the current project (or `codegraph stop <path>`, or `codegraph stop --all` to stop every daemon on the machine). Previously the only way to shut a daemon down was to hunt for its pid and `kill` it by hand. (#845)
 - The CodeGraph MCP server now self-heals if its main thread ever locks up. A lightweight watchdog notices when the process has stopped responding and stops it so a fresh one starts on your next request — it can no longer sit pinned at 100% CPU with no way to recover. Tune the detection window with `CODEGRAPH_WATCHDOG_TIMEOUT_MS`, or turn it off entirely with `CODEGRAPH_NO_WATCHDOG=1`. (#850)
 
 ### Fixes