Add Ful-Text Search and additional sdk rules

[DavideDelVecchio]

Summary

This issue tracks the addition of 10 new individual rule files corresponding to the rules
already added inline to AGENTS.md in the feat/sdk-rules-and-fulltext-search branch.

New SDK Rule Files (4.21–4.24)

File	Rule
sdk-conditional-create-etag.md	4.21 — Use IfNoneMatchETag("*") for conditional creates to prevent duplicates
sdk-request-options-per-call.md	4.22 — Never share a CosmosItemRequestOptions instance across multiple createItem calls
sdk-patch-counter-increment.md	4.23 — Use the Patch API for atomic counter increments
sdk-continuation-token-null-guard.md	4.24 — Guard against empty continuation tokens before calling byPage

New Full-Text Search Rule Files (12.1–12.6)

A new fts- prefix is introduced for the Full-Text Search category (Section 12).

File	Rule
fts-enable-capability.md	12.1 — Enable EnableNoSQLFullTextSearch capability on account
fts-define-policy.md	12.2 — Define fullTextPolicy on the container with correct language casing
fts-add-index.md	12.3 — Add fullTextIndexes entry in the indexing policy
fts-keyword-matching.md	12.4 — Use FullTextContains / ContainsAll / ContainsAny for keyword matching
fts-relevance-ranking.md	12.5 — Use FullTextScore with ORDER BY RANK for BM25 relevance ranking
fts-hybrid-queries.md	12.6 — Combine FTS predicates with range/equality filters for hybrid queries

Other Changes

• _sections.md updated with Section 12 (Full-Text Search / fts prefix)
• AGENTS.md regenerated (85 rules compiled)
• All 10 new rule files pass npm run validate

Branch

feat/sdk-rules-and-fulltext-search

[sajeetharan]

Thanks for raising the issue! please consider adding this to ideas!