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.

server/__tests__/lanes-lib.test.js

@@ -1269,3 +1269,21 @@ describe("the forward-only hold is short enough for one work session", () => {
     assert.equal(result, null);
   });
 });
+
+describe("createLane — canonical cwd (macOS /tmp -> /private/tmp class)", () => {
+  it("stores the realpath of a symlinked dir, and the given string when it does not exist yet", () => {
+    const fs = require("node:fs");
+    const base = fs.realpathSync(fs.mkdtempSync(pathMod.join(os.tmpdir(), "lane-realpath-")));
+    const target = pathMod.join(base, "real");
+    const link = pathMod.join(base, "link");
+    fs.mkdirSync(target);
+    fs.symlinkSync(target, link);
+    try {
+      assert.equal(lanes.createLane({ cwd: link + "/" }).cwd, target);
+      const missing = pathMod.join(base, "not-yet");
+      assert.equal(lanes.createLane({ cwd: missing }).cwd, missing);
+    } finally {
+      fs.rmSync(base, { recursive: true, force: true });
+    }
+  });
+});