fix: replace hardcoded localhost:3001 with relative API URL + add canvas mock and integration test

- Fix frontend Network error: API_BASE now defaults to empty string (same-origin)
- Fix 3 files: api.ts, AuthContext.tsx, Dashboard.tsx
- Add Canvas 2D context mock in tests/setup.ts for jsdom
- Fix -0 vs +0 in ZoomPanController.getViewport()
- Add IntegrationWorkflow.test.ts (35 tests, full CAD workflow)

backend/tests/settings.test.ts

@@ -0,0 +1,129 @@
+/**
+ * Settings API Tests – Key/Value settings (Get / Put / Upsert)
+ */
+import { describe, it, expect, beforeAll, afterAll } from 'vitest';
+import type { FastifyInstance } from 'fastify';
+import { SqliteAdapter } from '../src/database/SqliteAdapter.js';
+import { createServer } from '../src/server.js';
+
+describe('Settings API', () => {
+  let app: FastifyInstance;
+  let db: SqliteAdapter;
+
+  beforeAll(async () => {
+    db = new SqliteAdapter(':memory:');
+    await db.init();
+    app = await createServer({ db, port: 0 });
+    await app.ready();
+  });
+
+  afterAll(async () => {
+    await app.close();
+    db.close();
+  });
+
+  // ─── Get (missing key → 404) ─────────────────────────
+
+  describe('GET /api/settings/:key', () => {
+    it('should return 404 for non-existent setting', async () => {
+      const response = await app.inject({
+        method: 'GET',
+        url: '/api/settings/non-existent-key',
+      });
+      expect(response.statusCode).toBe(404);
+      const body = JSON.parse(response.body);
+      expect(body.error).toContain('Setting not found');
+    });
+
+    it('should return a setting that was previously set', async () => {
+      // First set a value
+      await app.inject({
+        method: 'PUT',
+        url: '/api/settings/test-key',
+        payload: { value: 'test-value' },
+      });
+
+      const response = await app.inject({
+        method: 'GET',
+        url: '/api/settings/test-key',
+      });
+      expect(response.statusCode).toBe(200);
+      const body = JSON.parse(response.body);
+      expect(body.key).toBe('test-key');
+      expect(body.value).toBe('test-value');
+      expect(body.updated_at).toBeDefined();
+    });
+  });
+
+  // ─── Put (upsert) ───────────────────────────────────
+
+  describe('PUT /api/settings/:key', () => {
+    it('should create a new setting', async () => {
+      const response = await app.inject({
+        method: 'PUT',
+        url: '/api/settings/new-setting',
+        payload: { value: 'new-value' },
+      });
+      expect(response.statusCode).toBe(200);
+      const body = JSON.parse(response.body);
+      expect(body.key).toBe('new-setting');
+      expect(body.value).toBe('new-value');
+      expect(body.updated_at).toBeDefined();
+    });
+
+    it('should update an existing setting (upsert)', async () => {
+      // Create initial
+      await app.inject({
+        method: 'PUT',
+        url: '/api/settings/upsert-key',
+        payload: { value: 'initial' },
+      });
+
+      // Update it
+      const response = await app.inject({
+        method: 'PUT',
+        url: '/api/settings/upsert-key',
+        payload: { value: 'updated' },
+      });
+      expect(response.statusCode).toBe(200);
+      const body = JSON.parse(response.body);
+      expect(body.key).toBe('upsert-key');
+      expect(body.value).toBe('updated');
+
+      // Verify via GET
+      const getRes = await app.inject({
+        method: 'GET',
+        url: '/api/settings/upsert-key',
+      });
+      const getBody = JSON.parse(getRes.body);
+      expect(getBody.value).toBe('updated');
+    });
+
+    it('should reject setting without value', async () => {
+      const response = await app.inject({
+        method: 'PUT',
+        url: '/api/settings/no-value-key',
+        payload: {},
+      });
+      const body = JSON.parse(response.body);
+      expect(body.error).toContain('Value is required');
+    });
+
+    it('should handle complex JSON values', async () => {
+      const complexValue = JSON.stringify({ nested: { object: true }, array: [1, 2, 3] });
+      const response = await app.inject({
+        method: 'PUT',
+        url: '/api/settings/complex-config',
+        payload: { value: complexValue },
+      });
+      expect(response.statusCode).toBe(200);
+
+      const getRes = await app.inject({
+        method: 'GET',
+        url: '/api/settings/complex-config',
+      });
+      const body = JSON.parse(getRes.body);
+      expect(body.value).toBe(complexValue);
+    });
+  });
+});