fix(validation): resolve merge conflicts with upstream/main

Rebased onto upstream/main which had evolved schemas.ts significantly:
- Upstream added imageUrlSchema for base64 data URL support
- Upstream tightened title (min 4, max 80) and description (min 20, max 500)
- Upstream added parseTimelineQuery, comment schemas, parseAssetCodes,
  parseIso8601Timestamp, typed field param in parsePositiveIntegerQueryParam,
  include_archived alias for includeDeleted, and a full parseCampaignListQuery

Our additions carried forward on top:
- validateBody returns 422 (was 400) - tests updated to match
- updateMetadataPayloadSchema using upstream constraint levels
- PATCH /api/campaigns/:id/metadata route in index.ts (unchanged)

Author: Wraith Protocol Dev

backend/src/middleware/validateBody.test.ts

@@ -62,9 +62,7 @@ describe('validateBody', () => {
   });
 
   it('returns 422 with the Validation failed shape when a field has the wrong type', async () => {
-    const response = await request(buildApp())
-      .post('/echo')
-      .send({ name: 'goal', age: 'one' });
+    const response = await request(buildApp()).post('/echo').send({ name: 'goal', age: 'one' });
 
     expect(response.status).toBe(422);
     expect(response.body.error).toBe('Validation failed');