test: add self-contained integration environment

Separate schema migrations from environment-specific fixtures, run the full API workflow against a disposable PostgreSQL Testcontainer, and provide seeded development and UI test environments.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

.github/workflows/ci.yml

@@ -0,0 +1,26 @@
+name: CI
+
+on:
+  push:
+  pull_request:
+
+permissions:
+  contents: read
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v5
+      - uses: actions/setup-go@v6
+        with:
+          go-version-file: backend/go.mod
+          cache-dependency-path: backend/go.sum
+      - uses: actions/setup-node@v5
+        with:
+          node-version: 26
+          cache: npm
+          cache-dependency-path: frontend/package-lock.json
+      - run: make test
+      - run: make lint
+      - run: make build