Add HTTP method/body, alert escalation, baseline alerts, notification grouping, rate limiting, App.js split, and API tests

- HTTP method + request body: GET/POST/PUT/PATCH/DELETE/HEAD selector and body textarea for http/health checks; stored in http_method/http_body columns; monitorService sends correct axios method+data
- Alert escalation: incidents open longer than escalation_hours get forwarded to fallback_webhook and marked escalated=1; hourly cron in scheduler
- Baseline-relative slow alerts: effectiveThreshold = response_time_threshold || (baseline * 2) — adaptive threshold without manual config
- Notification grouping: pendingAlerts collected per check cycle; ≥2 alerts flush as one grouped email+webhook; individual in-app entries still saved per resource
- Rate limiting: in-memory per-IP limiter (20/min heartbeat, 60/min status-page); no external package
- App.js split: Dashboard.js (monitors list + modals) and ResourceDetail.js extracted; App.js reduced from ~1987 to ~80 lines
- formatDuration moved to utils/timeUtils.js; imported by both new components
- DB migrations: http_method, http_body, incidents.escalated columns
- 18 passing API/unit tests (node:test, zero dependencies)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

client/build/asset-manifest.json

@@ -1,15 +1,15 @@
 {
   "files": {
-    "main.css": "/static/css/main.6034edfe.css",
-    "main.js": "/static/js/main.16dc004f.js",
+    "main.css": "/static/css/main.40bbff16.css",
+    "main.js": "/static/js/main.a387bcf0.js",
     "static/js/453.d456ce70.chunk.js": "/static/js/453.d456ce70.chunk.js",
     "index.html": "/index.html",
-    "main.6034edfe.css.map": "/static/css/main.6034edfe.css.map",
-    "main.16dc004f.js.map": "/static/js/main.16dc004f.js.map",
+    "main.40bbff16.css.map": "/static/css/main.40bbff16.css.map",
+    "main.a387bcf0.js.map": "/static/js/main.a387bcf0.js.map",
     "453.d456ce70.chunk.js.map": "/static/js/453.d456ce70.chunk.js.map"
   },
   "entrypoints": [
-    "static/css/main.6034edfe.css",
-    "static/js/main.16dc004f.js"
+    "static/css/main.40bbff16.css",
+    "static/js/main.a387bcf0.js"
   ]
 }