feat: startup environment check + self-heal (v1.3)

- env_check(): verifies daemon/pineapd/UCI/monitors/recon DB, auto-fixes
  fixable issues and re-verifies; forces runtime SSID-pool broadcast off to
  match the UI (kills the 'pool on but UI shows off' gap)
- server.py --env-check CLI; payload.sh runs it verbosely before starting,
  aborts on core failure
- serve() runs the check at every startup (boot + procd respawn)
- /api/health exposes env report + pool_runtime; /api/recon/status exposes
  wlan0_pinned (2.4GHz under-sampling warning); recon page warns when a
  radio0 AP pins wlan0mon
- recon start failures now include the daemon reason in the UI error
- shared stabilization refactor (_stabilize_uci/PINEAPD_SAFE_UCI/_raise_monitors)
- tests: test_env_check.py (18) + health/recon updates

README.md

@@ -51,6 +51,13 @@ Then on the Pager menu, run **Mark VIII**:
 - Re-run the payload while running to **Stop** the service.
 - `PAYLOAD_GET_CONFIG pager_webui auto_mode/run_mode` skip the prompt.
 
+Every payload run (and every service startup) first runs an **environment
+check** that prints on the payload screen / `/tmp/pagerwebui.log`: daemon
+reachable, pineapd alive, sane-off PineAP UCI defaults applied (SSID pool
+broadcast off, 6GHz hopper disabled, monitor bands), runtime pool sync, monitor
+interfaces up, and recon DB readable. Anything fixable is fixed and re-verified;
+startup aborts only if a core dependency fails.
+
 Browse `http://172.16.52.1:8080/` and log in with the device password.
 
 ## Uninstall / recovery