fix(cli): validate local anchor links

[kadymov]

Description

• validate local Markdown link fragments through the existing YFM002 rule
• collect rendered anchor IDs for automatic, explicit, duplicate, block, and included anchors
• preserve YFM003 precedence for missing or unreachable target pages
• avoid a duplicate YFM010 diagnostic for an autotitle whose anchor is missing
• invalidate the anchor cache when page or included content changes

How to test

npm test
npm run typecheck
npm run lint
npm run e2e

Focused regression checks:

npm test -- src/commands/build/services/anchors/AnchorsService.spec.ts src/commands/build/features/output-html/plugins/links.spec.ts
npm run e2e -- tests/e2e/errors.spec.ts

All commands above passed locally. The lint command reports four pre-existing warnings in src/commands/build/services/entry/EntryService.ts and no errors.

Tracker: DOCSTOOLS-6419

[sonarqubecloud]

Quality Gate failed

Failed conditions
77.9% Coverage on New Code (required ≥ 80%)

See analysis details on SonarQube Cloud