refactor: inline packages/db and packages/types into api package

Phase 2 extraction: groombook/api from groombook/app monorepo.

Changes:
- Move packages/db content to apps/api/src/db/
- Move packages/types content to apps/api/src/types/
- Inline database schema and migrations into api package
- Update Dockerfile to build single package
- Update CI workflow for single-package structure
- Fix vitest.config.ts aliases

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/api/migrations/0027_refunds.sql

@@ -0,0 +1,11 @@
+CREATE TABLE "refunds" (
+  "id" uuid PRIMARY KEY DEFAULT gen_random_uuid(),
+  "invoice_id" uuid NOT NULL REFERENCES "invoices"("id") ON DELETE RESTRICT,
+  "stripe_refund_id" text NOT NULL,
+  "idempotency_key" text UNIQUE,
+  "amount_cents" integer,
+  "created_at" timestamp NOT NULL DEFAULT NOW()
+);
+
+CREATE INDEX "idx_refunds_invoice_id" ON "refunds"("invoice_id");
+CREATE INDEX "idx_refunds_idempotency_key" ON "refunds"("idempotency_key");