fix(p0): resolve active domain automatically when onboarding skipped

- New resolveActiveDomain() helper in apps/web/lib/auth.ts: returns the
  user's first existing domain (ordered by sort_order then created_at),
  or auto-creates a default 'Personal' domain if they have none.
- 7 affected API routes (agents, canvases, domains, habits, projects,
  search, tasks) now fall back to resolveActiveDomain when the request
  omits a domain param. This eliminates the UNDEFINED_VALUE on domain_id
  and 22P02 invalid uuid errors that broke 6+ UI flows.
- New POST /api/quick-capture route: switches on type=task|habit|note|project
  to create the right entity, after resolving the active domain. This is
  the API the dashboard quick-capture widget calls.
- packages/db/src/schema.ts: added ownerId: uuid('owner_id') to the
  domains table so each user owns their domains.
- drizzle/0004_add_owner_id_to_domains.sql: matching migration with
  column add + index.
- apps/web/__tests__/lib/auth.test.ts: unit tests for both branches of
  resolveActiveDomain (returns existing / creates Personal).
- apps/web/app/(dashboard)/canvas/page.tsx: removed hardcoded
  domain: 'personal' from the quick-create payload so server-side
  resolution can do its job.

This unblocks all of: /tasks, /habits, /projects, /search, /settings/agents,
/settings/domains, /canvas, and dashboard quick-capture.

apps/web/app/api/search/route.ts

@@ -4,7 +4,7 @@
 // See AGENTS.md for full rules.
 
 import { NextRequest, NextResponse } from 'next/server';
-import { withAuth, createErrorResponse } from '@/lib/auth';
+import { withAuth, createErrorResponse, resolveActiveDomain } from '@/lib/auth';
 import { searchEntities } from '@/lib/search-service';
 
 // GET /api/search?q=&type=&domain=&limit=&offset=
@@ -13,7 +13,11 @@ export const GET = withAuth(async (request: NextRequest, user) => {
   const { searchParams } = new URL(request.url);
   const q = (searchParams.get('q') || '').trim();
   const types = searchParams.get('types')?.split(',').filter(Boolean) || ['task', 'note', 'project', 'habit', 'domain'];
-  const domain = searchParams.get('domain') || undefined;
+  let domain = searchParams.get('domain') || undefined;
+  if (!domain) {
+    const active = await resolveActiveDomain(user);
+    domain = active.id;
+  }
   const limit = Math.max(1, Math.min(50, parseInt(searchParams.get('limit') || '20')));
   const offset = Math.max(0, parseInt(searchParams.get('offset') || '0'));