feat: WireGuard metrics collector + integration test stack

Metrics collector (wiregui/collector.py):
- Standalone process spawned by web app when WG_METRICS_ENABLED=true
- Polls wg show dump every WG_METRICS_POLL_INTERVAL seconds (default 5)
- Updates device stats in PostgreSQL
- Pushes Prometheus-format metrics to VictoriaMetrics (if configured)
- Graceful shutdown on SIGTERM

Integration test stack (compose.yml):
- Unified compose file for dev, test, and integration modes
- VictoriaMetrics single-node TSDB for metrics storage
- 3 mock WireGuard client containers generating ping traffic
- Automated setup script seeds server keypair, admin user, client devices
- make test-stack-up: one command to start everything
- make test-stack-verify: validates metrics flowing end-to-end

Infrastructure:
- Makefile with targets for dev, test, integration, and production
- Integration tests verify VictoriaMetrics has data for all 3 clients
- Fix Dockerfile to include img/ directory
- Separate TESTS.md for test tracking, clean TODO.md for features only

.forgejo/workflows/dev.yml

@@ -66,7 +66,7 @@ jobs:
         run: uv run alembic upgrade head
 
       - name: Run unit tests
-        run: uv run pytest tests/ --ignore=tests/e2e -v --tb=short
+        run: uv run pytest tests/ --ignore=tests/e2e --ignore=tests/integration -v --tb=short
 
       - name: Run E2E tests
         run: uv run pytest tests/e2e/ -v --tb=short

.forgejo/workflows/release.yml

@@ -67,7 +67,7 @@ jobs:
         run: uv run alembic upgrade head
 
       - name: Run unit tests
-        run: uv run pytest tests/ --ignore=tests/e2e -v --tb=short
+        run: uv run pytest tests/ --ignore=tests/e2e --ignore=tests/integration -v --tb=short
 
       - name: Run E2E tests
         run: uv run pytest tests/e2e/ -v --tb=short