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/domains/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 { db, domains } from '@project-e/db';
 import { and, asc, desc, eq, ilike, or, sql } from 'drizzle-orm';
 import { z } from 'zod';
@@ -18,7 +18,7 @@ const createDomainSchema = z.object({
 });
 
 // GET /api/domains — List domains with filtering, sorting, pagination
-export const GET = withAuth(async (request: NextRequest, _user) => {
+export const GET = withAuth(async (request: NextRequest, user) => {
   const { searchParams } = new URL(request.url);
   const page = Math.max(1, parseInt(searchParams.get('page') || '1'));
   const perPage = Math.min(100, Math.max(1, parseInt(searchParams.get('perPage') || '50')));
@@ -39,8 +39,8 @@ export const GET = withAuth(async (request: NextRequest, _user) => {
     ? asc(sortColumns[sortField] || domains.sortOrder)
     : desc(sortColumns[sortField] || domains.sortOrder);
 
-  // Build where clause
-  const conditions: any[] = [];
+  // Build where clause — filter by owner
+  const conditions: any[] = [eq(domains.ownerId, user.id)];
   if (filter) {
     conditions.push(
       or(
@@ -64,7 +64,31 @@ export const GET = withAuth(async (request: NextRequest, _user) => {
       .where(and(...conditions)),
   ]);
 
-  const totalItems = Number(countResult[0]?.count || 0);
+  let totalItems = Number(countResult[0]?.count || 0);
+
+  // If user has no domains, auto-create a default "Personal" domain
+  if (totalItems === 0) {
+    const active = await resolveActiveDomain(user);
+    // Re-fetch to include the newly created domain
+    const [newItems, newCount] = await Promise.all([
+      db.select()
+        .from(domains)
+        .where(eq(domains.ownerId, user.id))
+        .orderBy(orderBy)
+        .limit(perPage)
+        .offset(offset),
+      db.select({ count: sql<number>`count(*)` })
+        .from(domains)
+        .where(eq(domains.ownerId, user.id)),
+    ]);
+    return NextResponse.json({
+      items: newItems,
+      totalItems: Number(newCount[0]?.count || 0),
+      totalPages: Math.ceil(Number(newCount[0]?.count || 0) / perPage),
+      page,
+      perPage,
+    });
+  }
 
   return NextResponse.json({
     items,
@@ -76,7 +100,7 @@ export const GET = withAuth(async (request: NextRequest, _user) => {
 });
 
 // POST /api/domains — Create a domain
-export const POST = withAuth(async (request: NextRequest, _user) => {
+export const POST = withAuth(async (request: NextRequest, user) => {
   try {
     const body = await request.json();
     const data = createDomainSchema.parse(body);
@@ -88,6 +112,7 @@ export const POST = withAuth(async (request: NextRequest, _user) => {
         color: data.color || null,
         icon: data.icon || null,
         parentId: data.parentId || null,
+        ownerId: user.id,
       })
       .returning();