feat: add E2E test suite with nightly CI, fix dashboard Dockerfile

E2E Tests:
- 17 integration tests covering: health, repos CRUD, findings lifecycle,
  cascade delete (SAST + DAST + pentest), DAST targets, stats overview
- TestServer harness: spins up agent API on random port with isolated
  MongoDB database per test, auto-cleanup
- Added lib.rs to expose agent internals for integration tests
- Nightly CI workflow with MongoDB service container (3 AM UTC)

Tests verify:
- Repository add/list/delete + duplicate rejection + invalid ID handling
- Finding creation, filtering by severity/repo, status updates, bulk updates
- Cascade delete: repo deletion removes all DAST targets, pentest sessions,
  attack chain nodes, DAST findings, SAST findings, and SBOM entries
- DAST target CRUD and empty finding list
- Stats overview accuracy with zero and populated data

Also:
- Fix Dockerfile.dashboard: bump dioxus-cli 0.7.3 → 0.7.4 (compile fix)
- Fix clippy: allow new_without_default for pattern scanners

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

compliance-agent/tests/integration/mod.rs

@@ -1,4 +1,9 @@
-// Integration tests for the compliance-agent crate.
+// E2E / Integration tests for the compliance-agent API.
 //
-// Add tests that exercise the full pipeline, API handlers,
-// and cross-module interactions here.
+// These tests require a running MongoDB instance. Set TEST_MONGODB_URI
+// if it's not at the default `mongodb://root:example@localhost:27017`.
+//
+// Run with:   cargo test -p compliance-agent --test e2e
+// Or nightly: (via CI with MongoDB service container)
+
+mod api;