feat: add notifications and project shares features

- Backend: notifications + shares routes, DB tables, SqliteAdapter methods
- Frontend: NotificationPanel (bell icon + dropdown), ShareDialog, Dashboard integration
- Styles: notification + share dialog CSS

backend/src/database/schema.sql

@@ -105,3 +105,31 @@ CREATE INDEX IF NOT EXISTS idx_layers_drawing ON layers(drawing_id);
 CREATE INDEX IF NOT EXISTS idx_elements_drawing ON elements(drawing_id);
 CREATE INDEX IF NOT EXISTS idx_elements_layer ON elements(layer_id);
 CREATE INDEX IF NOT EXISTS idx_blocks_drawing ON blocks(drawing_id);
+ 
+ -- ─── Notifications ───────────────────────────────────
+ CREATE TABLE IF NOT EXISTS notifications (
+   id TEXT PRIMARY KEY,
+   user_id TEXT NOT NULL,
+   type TEXT NOT NULL DEFAULT 'info',
+   title TEXT NOT NULL,
+   message TEXT NOT NULL,
+   read INTEGER NOT NULL DEFAULT 0,
+   created_at TEXT NOT NULL DEFAULT (datetime('now')),
+   FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE
+ );
+ 
+ -- ─── Project Shares ──────────────────────────────────
+ CREATE TABLE IF NOT EXISTS project_shares (
+   id TEXT PRIMARY KEY,
+   project_id TEXT NOT NULL,
+   shared_with_email TEXT NOT NULL,
+   shared_by TEXT NOT NULL,
+   permission TEXT NOT NULL DEFAULT 'view' CHECK(permission IN ('view','edit','admin')),
+   share_token TEXT UNIQUE,
+   created_at TEXT NOT NULL DEFAULT (datetime('now')),
+   FOREIGN KEY (project_id) REFERENCES projects(id) ON DELETE CASCADE,
+   FOREIGN KEY (shared_by) REFERENCES users(id) ON DELETE CASCADE
+ );
+ 
+ CREATE INDEX IF NOT EXISTS idx_notifications_user ON notifications(user_id);
+ CREATE INDEX IF NOT EXISTS idx_shares_project ON project_shares(project_id);