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/routes/shares.ts

@@ -0,0 +1,67 @@
+/**
+ * Project Shares Routes – List, create, delete project shares
+ */
+import type { FastifyInstance } from 'fastify';
+import type { DatabaseInterface } from '../database/DatabaseInterface.js';
+import type { AuthService } from '../auth/AuthService.js';
+
+function extractToken(request: any): string | null {
+  const auth = request.headers?.authorization;
+  if (auth && auth.startsWith('Bearer ')) return auth.slice(7);
+  return null;
+}
+
+export function registerShareRoutes(fastify: FastifyInstance, db: DatabaseInterface, authService: AuthService) {
+  // List shares for a project
+  fastify.get('/api/projects/:projectId/shares', async (request, reply) => {
+    const token = extractToken(request);
+    if (!token) return reply.code(401).send({ error: 'Authentication required' });
+    const user = authService.getUserFromSession(token);
+    if (!user) return reply.code(401).send({ error: 'Invalid or expired session' });
+    const { projectId } = request.params as { projectId: string };
+    return db.listProjectShares(projectId);
+  });
+
+  // Create a project share
+  fastify.post('/api/projects/:projectId/shares', async (request, reply) => {
+    const token = extractToken(request);
+    if (!token) return reply.code(401).send({ error: 'Authentication required' });
+    const user = authService.getUserFromSession(token);
+    if (!user) return reply.code(401).send({ error: 'Invalid or expired session' });
+    const { projectId } = request.params as { projectId: string };
+    const body = request.body as { shared_with_email?: string; permission?: string };
+    if (!body.shared_with_email) return reply.code(400).send({ error: 'shared_with_email is required' });
+
+    const share = db.createProjectShare({
+      project_id: projectId,
+      shared_with_email: body.shared_with_email,
+      shared_by: user.id,
+      permission: body.permission ?? 'view',
+    });
+
+    // Create a notification for the shared user if they exist
+    const sharedUser = db.getUserByEmail(body.shared_with_email);
+    if (sharedUser) {
+      db.createNotification({
+        user_id: sharedUser.id,
+        type: 'share',
+        title: 'Projekt geteilt',
+        message: `${user.name} hat ein Projekt mit Ihnen geteilt: ${db.getProject(projectId)?.name ?? 'Unbenannt'}`,
+      });
+    }
+
+    return reply.code(201).send(share);
+  });
+
+  // Delete a project share
+  fastify.delete('/api/shares/:id', async (request, reply) => {
+    const token = extractToken(request);
+    if (!token) return reply.code(401).send({ error: 'Authentication required' });
+    const user = authService.getUserFromSession(token);
+    if (!user) return reply.code(401).send({ error: 'Invalid or expired session' });
+    const { id } = request.params as { id: string };
+    const ok = db.deleteProjectShare(id);
+    if (!ok) return reply.code(404).send({ error: 'Share not found' });
+    return reply.code(204).send();
+  });
+}