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.

scripts/plugin-bootstrap.js

@@ -359,13 +359,15 @@ function cliDir() {
  *
  * @returns {"written"|"exists"|"foreign"|"failed"}
  */
-function linkCli(dir = cliDir(), root = PLUGIN_ROOT) {
+function linkCli(dir = cliDir(), root = PLUGIN_ROOT, nodePath = process.execPath) {
   const marker = "# agenthub-plugin-launcher";
   const target = path.join(dir, process.platform === "win32" ? "agenthub.cmd" : "agenthub");
   const body =
     process.platform === "win32"
       ? `@rem agenthub-plugin-launcher\r\n@node "${path.join(root, "bin", "agenthub.js")}" %*\r\n`
-      : `#!/bin/sh\n${marker}\nexec "${process.execPath}" "${path.join(root, "bin", "agenthub.js")}" "$@"\n`;
+      : // The pinned node is a versioned path (Homebrew Cellar, nvm) that an
+        // upgrade deletes; fall back to whatever `node` PATH has then.
+        `#!/bin/sh\n${marker}\nN="${nodePath}"; [ -x "$N" ] || N=node\nexec "$N" "${path.join(root, "bin", "agenthub.js")}" "$@"\n`;
   try {
     if (fs.existsSync(target)) {
       const current = fs.readFileSync(target, "utf8");
@@ -419,7 +421,11 @@ function liveServers() {
   try {
     const parsed = JSON.parse(fs.readFileSync(getServerInfoPath(), "utf8"));
     const servers = Array.isArray(parsed.servers) ? parsed.servers : [parsed];
-    return servers.filter((s) => s && isPidAlive(s.pid));
+    // An entry older than this boot is a leftover whose pid may now belong to
+    // an unrelated process (macOS has no systemd to clean up after a reboot).
+    // 60 s margin for clock skew; an unparseable startedAt is kept.
+    const bootedAt = Date.now() - os.uptime() * 1000 - 60_000;
+    return servers.filter((s) => s && isPidAlive(s.pid) && !(Date.parse(s.startedAt) < bootedAt));
   } catch {
     return [];
   }