refactor: Modularize server into separate concerns

Split monolithic index.ts (~1400 lines) into modular structure:
- config.ts: Server configuration and constants
- db/: Database initialization, migrations, and seeds
- routes/: API handlers by domain (themes, canvas, components, etc.)
- services/: Terminal WebSocket server
- utils/: CORS helpers

Entry point now only coordinates initialization.

server/routes/components.ts

@@ -0,0 +1,84 @@
+import { db } from '../db'
+import { jsonResponse, errorResponse } from '../utils/cors'
+
+export async function handleComponents(req: Request) {
+  if (req.method === 'GET') {
+    const rows = db.query('SELECT * FROM vue_components ORDER BY updated_at DESC').all()
+    return jsonResponse(rows)
+  }
+
+  if (req.method === 'POST') {
+    const body = await req.json()
+    const id = body.id || `comp-${Date.now()}`
+    const stmt = db.prepare(`
+      INSERT OR REPLACE INTO vue_components
+      (id, name, template, setup, style, props, imports, updated_at)
+      VALUES (?, ?, ?, ?, ?, ?, ?, CURRENT_TIMESTAMP)
+    `)
+    stmt.run(
+      id,
+      body.name,
+      body.template,
+      body.setup || '',
+      body.style || '',
+      JSON.stringify(body.props || []),
+      JSON.stringify(body.imports || [])
+    )
+    return jsonResponse({ success: true, id })
+  }
+
+  if (req.method === 'DELETE') {
+    db.run('DELETE FROM vue_components')
+    return jsonResponse({ success: true })
+  }
+
+  return null
+}
+
+export async function handleComponentById(req: Request, id: string) {
+  if (req.method === 'GET') {
+    const row = db.query('SELECT * FROM vue_components WHERE id = ?').get(id)
+    if (!row) {
+      return errorResponse('Component not found', 404)
+    }
+    return jsonResponse(row)
+  }
+
+  if (req.method === 'DELETE') {
+    // Check if component is in use by any canvas
+    const usage = db.query(`
+      SELECT pc.id, pc.name
+      FROM canvas_components cc
+      JOIN project_canvas pc ON cc.canvas_id = pc.id
+      WHERE cc.component_id = ?
+    `).all(id) as { id: string; name: string }[]
+
+    if (usage.length > 0) {
+      return jsonResponse({
+        error: 'Component in use',
+        message: `Cannot delete component. It is used by: ${usage.map(u => u.name).join(', ')}`,
+        usedBy: usage
+      }, 409)
+    }
+
+    db.run('DELETE FROM vue_components WHERE id = ?', [id])
+    return jsonResponse({ success: true })
+  }
+
+  return null
+}
+
+export function handleComponentUsage(componentId: string) {
+  const usage = db.query(`
+    SELECT pc.id, pc.name, pc.type
+    FROM canvas_components cc
+    JOIN project_canvas pc ON cc.canvas_id = pc.id
+    WHERE cc.component_id = ?
+  `).all(componentId) as { id: string; name: string; type: string }[]
+
+  return jsonResponse({
+    componentId,
+    usedBy: usage,
+    canDelete: usage.length === 0
+  })
+}