Add integration e2e coverage: GitHubApp, advisory pipeline, Rekor, eBPF hardening

- GitHubApp: 11 new tests (health, CRUD lifecycle, update, delete, UI SCM tab)
- Advisory pipeline: 16 tests (fixture data verification, source management smoke,
  initial/incremental sync, cross-source merge, canonical query API, UI catalog)
  with KEV/GHSA/EPSS fixture data files for deterministic testing
- Rekor transparency: 7 tests (container health, submit/get/verify round-trip,
  log consistency, attestation API) gated behind E2E_REKOR=1
- eBPF agent: 3 edge case tests (unreachable endpoint, coexistence, degraded health)
  plus mock limitation documentation in test header
- Fix UI search race: wait for table rows before counting rowsBefore
- Advisory fixture now serves real data (KEV JSON, GHSA list, EPSS CSV)
- Runtime host fixture adds degraded health endpoint

Suite: 143 passed, 0 failed, 32 skipped in 13.5min (up from 123 tests)

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

devops/compose/docker-compose.integration-fixtures.yml

@@ -66,6 +66,7 @@ services:
       - "127.1.1.8:80:80"
     volumes:
       - ./fixtures/integration-fixtures/advisory/default.conf:/etc/nginx/conf.d/default.conf:ro
+      - ./fixtures/integration-fixtures/advisory/data:/etc/nginx/data:ro
     networks:
       stellaops:
         aliases: