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.

openapi.yaml

@@ -10636,7 +10636,7 @@ paths:
       tags:
         - Lanes
       summary: Find or adopt the lane owning a working directory
-      description: 'Idempotent: returns the lane whose cwd is an exact match or the longest path-boundary parent of `cwd` with `created: false` (200) — with `exact: true` only an exact match counts, so a directory nested inside another lane gets a lane of its own (the Add-lane modal sends it) — otherwise creates an `adopted` lane and returns it with `created: true` (201). The Workspace page opens on a directory rather than a lane id, so this is how it gets exactly one lane for that directory. Concurrent calls for the same path resolve to ONE lane: the `lanes.cwd` UNIQUE constraint decides, and the loser re-reads and returns the winner''s lane.'
+      description: 'Idempotent: canonicalizes `cwd` to its real path when it exists (the same path `createLane` stores), then returns the lane whose cwd is an exact match or the longest path-boundary parent of `cwd` with `created: false` (200) — with `exact: true` only an exact match counts, so a directory nested inside another lane gets a lane of its own (the Add-lane modal sends it) — otherwise creates an `adopted` lane and returns it with `created: true` (201). The Workspace page opens on a directory rather than a lane id, so this is how it gets exactly one lane for that directory. Concurrent calls for the same path resolve to ONE lane: the `lanes.cwd` UNIQUE constraint decides, and the loser re-reads and returns the winner''s lane.'
       operationId: ensureLane
       requestBody:
         required: true