docs: fix broken links and code examples; publish Java Javadoc in CI

[zantvoort]

Summary

Fixes several broken links and incorrect code examples across the docs and landing page, plus a CI bug that leaves the Java Javadoc unpublished on orm.st. Documentation changes are applied to docs/ and the latest versioned_docs/version-1.11.5 snapshot only (older snapshots left frozen).

Changes

• Landing page (src/pages/index.js) — the topCities generated-SQL panel now shows GROUP BY u.city_id instead of the expanded c.id, c.name, c.population, c.country. Verified against the framework: .groupBy(User_.city) on a single-column-PK @FK flattens to a single leaf and resolves to the foreign-key column on the driving table (same resolution as WHERE).
• getting-started.md / index.md — replaced broken absolute links /dirty-checking and /ai with relative doc links (docs are served under /docs, so root-absolute links 404).
• relationships.md — switched the many-to-one example to orm.get so it reads user.city.name. The previous orm.find + user?.city.name did not compile (safe-call chain on a nullable receiver).
• configuration.md — added an explicit {#schema-validation} anchor to the storm.validation.schema_mode heading so the five "Schema Validation" cross-references (spring-integration, faq ×2, entities, migration-from-jpa) resolve.
• faq.md — retargeted the deferred-loading link to refs.md#deferred-loading; entities.md#deferred-loading-with-ref did not exist.
• .github/workflows/docs.yml — the "Copy Javadoc" step guarded on target/reports/apidocs (Maven 4), but mvn javadoc:aggregate on the Maven 3.9.x runner writes to target/site/apidocs, so the copy silently no-opped and an empty static/api/java shipped. Now copies from either path and fails loudly if neither exists.

Verification

• Framework code + tests confirm the GROUP BY u.city_id behavior (testGroupByInlineRecord asserts the FK leaf resolves to city_id).
• Link-checked docs/ and version-1.11.5 — all in-content links now resolve.
• Probed the live site: /api/java/index.html returns 404, all five /api/kotlin/<module>/index.html return 200. The workflow fix addresses the Java 404 on the next docs deploy.