fix(macos): scrub parent-session env, survive node upgrades and reboots, store lanes by real path (#22)

What broke (code audit, untested on a Mac):
- Without systemd the server is always spawned from inside a Claude Code
  session, so it inherited CLAUDECODE, CLAUDE_CODE_SESSION_ID,
  CLAUDE_PLUGIN_ROOT, ... and tmux handed them to every lane pane (a codex
  pane even resolved as `claude` in `agenthub`'s harness check).
- The ~/.local/bin/agenthub launcher pinned a versioned node path that
  `brew upgrade`/nvm deletes, leaving the CLI dead until the next bootstrap.
- A discovery entry left over from before a reboot could name a recycled pid,
  so the bootstrap's fast path believed a dashboard was live and
  stopDashboard could signal an unrelated process.
- Lanes were stored under the typed cwd; macOS reports /private/tmp and the
  on-disk case, so sessions never bound to a /tmp or differently-cased lane.

What changed:
- server/index.js deletes a DENYLIST of parent-session variables at startup;
  user config (CLAUDE_CONFIG_DIR, CLAUDE_CODE_USE_BEDROCK, ANTHROPIC_*) stays.
- linkCli's launcher falls back to `node` on PATH when the pinned one is gone.
- liveServers ignores entries whose startedAt predates this boot (60 s margin).
- createLane and POST /api/lanes/ensure store/look up fs.realpathSync.native
  of an existing cwd; the liveness reaper also tries the realpath. Existing
  rows are untouched.
- session-liveness gains an exec seam so the darwin ps+lsof branch is tested.
- plugin-doctor names ~/.zshrc on darwin; INSTALL.md gains a macOS section
  with the Mac verification checklist, mirrored in both READMEs and PLUGINS.md.
No launchd, no macOptionIsMeta, engines stays >=20.

docs/LANES.md

@@ -22,7 +22,7 @@ agenthub lanes add --cwd /path/to/repo --title "My Feature"
 
 The lane is now ready to track work. When you run a Claude Code session in that directory (or a subdirectory), the dashboard will bind the session to the lane automatically by matching the cwd.
 
-**Note:** The directory must exist and be an absolute path. A lane with a cwd of `/tmp/wt` will NOT capture `/tmp/wt-sibling` (no partial prefix match) but WILL capture sessions in `/tmp/wt/subdir/` (subdirectories are owned by the parent lane unless a deeper lane exists).
+**Note:** The directory must exist and be an absolute path. A lane with a cwd of `/tmp/wt` will NOT capture `/tmp/wt-sibling` (no partial prefix match) but WILL capture sessions in `/tmp/wt/subdir/` (subdirectories are owned by the parent lane unless a deeper lane exists). A `cwd` that exists is stored by its real path (`fs.realpathSync.native`), so `/tmp/wt` on macOS is stored as `/private/tmp/wt` and a differently-cased path on a case-insensitive volume as the spelling on disk — the path a session reports. A path that does not exist yet keeps the string it was given; rows created before this rule keep theirs.
 
 To provision a dashboard-managed git worktree instead of adopting an existing directory, use a source repository: