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>

server/database.js

@@ -311,6 +311,13 @@ try {
   db.prepare("INSERT OR IGNORE INTO settings (key, value) VALUES ('incident_failure_threshold', '10')").run();
 } catch (err) {}
 
+// Feature: HTTP method + request body support
+try { db.prepare("ALTER TABLE resources ADD COLUMN http_method TEXT DEFAULT 'GET'").run(); } catch(e) {}
+try { db.prepare("ALTER TABLE resources ADD COLUMN http_body TEXT").run(); } catch(e) {}
+
+// Feature: alert escalation tracking
+try { db.prepare("ALTER TABLE incidents ADD COLUMN escalated INTEGER DEFAULT 0").run(); } catch(e) {}
+
 // Feature: heartbeat / cron-job monitoring
 try { db.prepare("ALTER TABLE resources ADD COLUMN heartbeat_token TEXT").run(); } catch(e) {}
 try { db.prepare("ALTER TABLE resources ADD COLUMN heartbeat_timeout INTEGER DEFAULT 300000").run(); } catch(e) {}