feat: create themes table and migrate content settings from settings

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CLAUDE.md

@@ -117,7 +117,7 @@ cd frontend && npx tsc --noEmit
 - `GET /api/v1/admin/users` — user list
 - `PUT /api/v1/admin/users/:id/role` — role management
 
-## Database (27 migrations)
+## Database (28 migrations)
 Tables: `users`, `sessions`, `magic_link_tokens`, `user_settings`, `sources`, `syntheses`, `admin_providers`, `admin_rate_limits`, `user_api_keys`, `audit_log`
 
 ## Environment Variables

backend/migrations/20260326000028_create_themes_and_migrate.sql

@@ -0,0 +1,44 @@
+-- 1. Create themes table
+CREATE TABLE themes (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    user_id UUID NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    name TEXT NOT NULL,
+    theme TEXT NOT NULL,
+    categories JSONB NOT NULL DEFAULT '[]',
+    max_items_per_category INTEGER NOT NULL DEFAULT 4,
+    max_age_days INTEGER NOT NULL DEFAULT 7,
+    summary_length INTEGER NOT NULL DEFAULT 3,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT now(),
+    updated_at TIMESTAMPTZ NOT NULL DEFAULT now()
+);
+CREATE INDEX idx_themes_user_id ON themes(user_id);
+
+-- 2. Migrate existing settings to default themes
+INSERT INTO themes (user_id, name, theme, categories, max_items_per_category, max_age_days, summary_length)
+SELECT user_id, theme, theme, categories, max_items_per_category, max_age_days, summary_length
+FROM settings;
+
+-- 3. Add theme_id to sources (nullable)
+ALTER TABLE sources ADD COLUMN theme_id UUID REFERENCES themes(id) ON DELETE CASCADE;
+
+-- 4. Backfill sources with the user's default theme
+UPDATE sources s
+SET theme_id = t.id
+FROM themes t
+WHERE s.user_id = t.user_id;
+
+-- 5. Add theme_id to syntheses (nullable, SET NULL on theme deletion)
+ALTER TABLE syntheses ADD COLUMN theme_id UUID REFERENCES themes(id) ON DELETE SET NULL;
+
+-- 6. Backfill syntheses with the user's default theme
+UPDATE syntheses sy
+SET theme_id = t.id
+FROM themes t
+WHERE sy.user_id = t.user_id;
+
+-- 7. Drop moved columns from settings
+ALTER TABLE settings DROP COLUMN theme;
+ALTER TABLE settings DROP COLUMN categories;
+ALTER TABLE settings DROP COLUMN max_items_per_category;
+ALTER TABLE settings DROP COLUMN max_age_days;
+ALTER TABLE settings DROP COLUMN summary_length;