[Docs cleanup] Update validation tooling guides to target generated OpenAPI

[lirenhe]

Context: LintDiff/Spectral, OAV, and OAD still run — but on OpenAPI generated from TypeSpec. Guidance
that installs/runs AutoRest, or that tells authors to hand-edit Swagger, is out of date. This issue tracks
rewording these guides (and deleting items that no longer used).

Legend: 🔴 OBSOLETE (delete/archive) · 🟡 NEEDS-UPDATE (reword)

Tasks:

• 🔴 documentation/SwaggerValidationTools.md — obsolete (npm install -g autorest --azure-validator); rewrite to LintDiff/OAV/OAD entrypoints
• 🟡 documentation/openapi-authoring-automated-guidelines.md (LintDiff/Spectral rules) — reframe as rules for generated OpenAPI; fix AutoRest links
• 🟡 documentation/Semantic-and-Model-Violations-Reference.md (OAV) — keep catalog, change "fix in swagger" → "fix TypeSpec / generated OpenAPI"
• 🟡 documentation/ci-fix.md — split TypeSpec vs generated-OpenAPI checks; drop swagger-authoring assumptions
• 🟡 documentation/FAQ.md — stop presenting Swagger as authoring source; keep validation links
• 🟡 documentation/swagger-accuracy-report.md (RESTler + OAV) — rename swagger wording; process still valid