Add backend foundation and config-driven workbench

backend/migrations/0003_home.sql

@@ -0,0 +1,32 @@
+BEGIN;
+
+CREATE TABLE cards (
+  id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+  card_public_id TEXT NOT NULL UNIQUE,
+  tenant_id UUID NOT NULL REFERENCES tenants(id) ON DELETE CASCADE,
+  entry_channel_id UUID REFERENCES entry_channels(id) ON DELETE SET NULL,
+  card_type TEXT NOT NULL CHECK (card_type IN ('event', 'html', 'notice')),
+  title TEXT NOT NULL,
+  subtitle TEXT,
+  cover_url TEXT,
+  event_id UUID REFERENCES events(id) ON DELETE SET NULL,
+  html_url TEXT,
+  display_slot TEXT NOT NULL DEFAULT 'home_primary',
+  display_priority INTEGER NOT NULL DEFAULT 0,
+  status TEXT NOT NULL DEFAULT 'active' CHECK (status IN ('draft', 'active', 'disabled', 'archived')),
+  starts_at TIMESTAMPTZ,
+  ends_at TIMESTAMPTZ,
+  created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+  updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+CREATE INDEX cards_tenant_id_idx ON cards(tenant_id);
+CREATE INDEX cards_entry_channel_id_idx ON cards(entry_channel_id);
+CREATE INDEX cards_event_id_idx ON cards(event_id);
+CREATE INDEX cards_display_idx ON cards(display_slot, status, display_priority DESC);
+
+CREATE TRIGGER cards_set_updated_at
+BEFORE UPDATE ON cards
+FOR EACH ROW EXECUTE FUNCTION set_updated_at();
+
+COMMIT;