feat: add server lifecycle management and D1 logging

- Add start/stop/reboot endpoints for server power management
- Add D1-based logging system (logs table + db-logger utility)
- Add idempotency_key validation for order deduplication
- Extend VPS provider interface with lifecycle methods

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

migrations/005_add_logs_table.sql

@@ -0,0 +1,13 @@
+-- D1 로깅 테이블
+CREATE TABLE IF NOT EXISTS logs (
+  id INTEGER PRIMARY KEY AUTOINCREMENT,
+  level TEXT NOT NULL,
+  service TEXT NOT NULL,
+  message TEXT NOT NULL,
+  context TEXT,
+  created_at TEXT DEFAULT (datetime('now'))
+);
+
+CREATE INDEX IF NOT EXISTS idx_logs_created ON logs(created_at DESC);
+CREATE INDEX IF NOT EXISTS idx_logs_level ON logs(level);
+CREATE INDEX IF NOT EXISTS idx_logs_service ON logs(service);