feat: Add canvas snapshots to save and restore full canvas state

Implements save/restore system that captures HTML base, injected CSS,
executed scripts, and floating Vue windows with their full definitions.
Adds 4 MCP tools, backend CRUD API, Pinia store, and script logger.

server/db/migrations.ts

@@ -85,6 +85,17 @@ export function runMigrations(db: Database) {
     )
   `)
 
+  // Canvas snapshots table
+  db.run(`
+    CREATE TABLE IF NOT EXISTS canvas_snapshots (
+      id TEXT PRIMARY KEY,
+      name TEXT NOT NULL,
+      data TEXT NOT NULL,
+      thumbnail TEXT,
+      created_at INTEGER NOT NULL
+    )
+  `)
+
   // Voice recordings table (for training custom speech models)
   db.run(`
     CREATE TABLE IF NOT EXISTS voice_recordings (