chore: add server provisioning migrations

- 003_add_server_tables.sql: server_orders, server_instances tables
- 003_server_sessions.sql: KV-based session tracking
- 004_add_terminated_at.sql: track instance termination time

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

migrations/003_server_sessions_d1.sql

@@ -0,0 +1,21 @@
+-- Migration 003: Server Sessions to D1 Database
+-- Migrate server session management from KV Namespace to D1 Database
+-- Date: 2026-01-28
+
+-- Create server_sessions table
+CREATE TABLE IF NOT EXISTS server_sessions (
+  user_id TEXT PRIMARY KEY,
+  status TEXT NOT NULL CHECK(status IN ('gathering', 'recommending', 'selecting', 'ordering', 'completed')),
+  collected_info TEXT,
+  last_recommendation TEXT,
+  messages TEXT,
+  created_at INTEGER NOT NULL,
+  updated_at INTEGER NOT NULL,
+  expires_at INTEGER NOT NULL
+);
+
+-- Create index for expiry cleanup
+CREATE INDEX IF NOT EXISTS idx_server_sessions_expires ON server_sessions(expires_at);
+
+-- Note: Existing KV sessions will be automatically migrated on first access
+-- Old sessions in KV will expire naturally (1 hour TTL)