Add Resources section with doc links to databricks-vector-search skill

[CheeYuTan]

Summary

• Adds a Resources section with 5 external documentation links (Vector Search overview, index creation, API reference, embedding models, retriever tool)
• The vector-search skill had Related Skills but no external documentation references

Test proof

Tested Vector Search patterns against live workspace e2-demo-field-eng:

Test	Result
List Vector Search endpoints	PASS — endpoints returned including active endpoints

TEST: List Vector Search endpoints
  PASS
  → [EndpointInfo(creation_timestamp=..., state=ONLINE, ...)]

Vector Search endpoint listing verified.

[calreynolds]

Closing — same as the Common Issues PRs, we'd prefer Related Skills/Resources additions consolidated into a single PR. Happy to review a combined version!