Add uptime monitor features: fix history bars, lifetime stats, detail modal, custom services

- Fix 24-bar history rendering to always show 24 uniform segments with gray fill for missing hours
- Add lifetime uptime % and avg latency to status API
- Add clickable detail modal with expanded stats, large history bar, and service removal
- Add monitored_services DB table with CRUD API (GET/POST/DELETE)
- Monitor reads services from DB each interval, seeds defaults on first run
- Add inline form to add custom services to track
- Extend log retention from 7 days to 90 days for lifetime stats

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

lib/db.ts

@@ -35,6 +35,13 @@ export async function getDb() {
       lon REAL,
       timestamp DATETIME DEFAULT CURRENT_TIMESTAMP
     );
+
+    CREATE TABLE IF NOT EXISTS monitored_services (
+      id INTEGER PRIMARY KEY AUTOINCREMENT,
+      name TEXT NOT NULL UNIQUE,
+      url TEXT NOT NULL,
+      created_at DATETIME DEFAULT CURRENT_TIMESTAMP
+    );
   `);
 
   return db;