feat: add session move endpoint and project-session cascading delete

- Add sessions table to database with projectId and deletedAt columns
- Create POST /api/sessions/:id/move endpoint to reassign sessions
- Update DELETE /api/projects/:id to cascade soft-delete to sessions
- Support moving sessions between projects or to unassigned state
- Handle both active (in-memory) and historical sessions

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

services/database.js

@@ -48,6 +48,26 @@ function initializeDatabase() {
     CREATE INDEX IF NOT EXISTS idx_projects_name ON projects(name)
   `);
 
+  // Create sessions table
+  db.exec(`
+    CREATE TABLE IF NOT EXISTS sessions (
+      id TEXT PRIMARY KEY,
+      projectId INTEGER NULL,
+      deletedAt TEXT NULL,
+      FOREIGN KEY (projectId) REFERENCES projects(id) ON DELETE SET NULL
+    )
+  `);
+
+  // Create index on projectId for efficient session queries
+  db.exec(`
+    CREATE INDEX IF NOT EXISTS idx_sessions_projectId ON sessions(projectId)
+  `);
+
+  // Create index on deletedAt for efficient soft-delete queries
+  db.exec(`
+    CREATE INDEX IF NOT EXISTS idx_sessions_deletedAt ON sessions(deletedAt)
+  `);
+
   return db;
 }