feat(seo-gap-analysis): add public SEO competitor gap analysis endpoint

[shrotia]

Adds the public async HTTP surface for the SEO/GEO/AEO competitor gap analysis feature:

• POST /seo-gap-analysis: validates { keyword, targetUrl, filterDomains?, currentRanking?, locale? }, creates an AsyncJob (jobType seo-gap-analysis), enqueues a message on AUDIT_JOBS_QUEUE_URL for the audit worker, and returns 202 + { jobId, pollUrl }. Modeled on the site-detection async controller.
• GET /seo-gap-analysis/jobs/:jobId: returns status + gap report, scoped to the seo-gap-analysis jobType via loadJobScopedToCaller (IDOR-safe).
• Route wiring in routes/index.js + controller instantiation in index.js.
• IMS + entitlement enforced declaratively: classified in required-capabilities (site:write / site:read) and facs-capabilities (llmo + aso, can_configure / can_view). jobId already lives in FACS_NON_RESOURCE_PARAMS.
• OpenAPI: docs/openapi/seo-gap-analysis-api.yaml + registration in api.yaml.
• Unit tests: 100% coverage on the controller (20 tests); all 3585 route drift tests pass with the new entries.

Companion branches of the same name in spacecat-audit-worker (SERP + scrape + diff handlers) and spacecat-content-scraper (seo-comparison scrape handler). Follow-up: integration tests under test/it/ (Docker/postgres seed harness).

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• make sure to link the related issues in this description. Or if there's no issue created, make sure you
  describe here the problem you're solving.
• when merging / squashing, make sure the fixed issue references are visible in the commits, for easy compilation of release notes

If the PR is changing the API specification:

• make sure you add a "Not implemented yet" note the endpoint description, if the implementation is not ready
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Related Issues

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This PR will trigger a minor release when merged.

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