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/index.js

@@ -5,6 +5,18 @@
 
 if (!process.env.NODE_ENV) process.env.NODE_ENV = "production";
 
+// A server started from inside a Claude Code session (the bootstrap fallback,
+// always the case on macOS) inherits that session's own variables, and tmux
+// hands them to every lane pane — whose `claude` then believes it is nested.
+// ponytail: a DENYLIST of parent-session variables only, so user config
+// (CLAUDE_CONFIG_DIR, CLAUDE_CODE_USE_BEDROCK, ANTHROPIC_*) passes through;
+// it must grow when Claude Code adds a new per-session variable.
+const PARENT_SESSION_VARS =
+  /^(CLAUDECODE|CLAUDE_PID|CLAUDE_PROJECT_DIR|CLAUDE_ENV_FILE|CLAUDE_PLUGIN_(ROOT|DATA)|CLAUDE_CODE_(ENTRYPOINT|SESSION_ID|CHILD_SESSION|SESSION_ATTENDED|EXECPATH|MESSAGING_.*))$/;
+for (const k of Object.keys(process.env)) {
+  if (PARENT_SESSION_VARS.test(k)) delete process.env[k];
+}
+
 // Load .env file (simple key=value, no external dependency needed)
 (function loadDotEnv() {
   const fs = require("fs");