Generate vector databases OpenAPI spec from proto (KBAAS-426)

[nbhoot157]

Replaces the hand-authored spec in #1181 with output from an automated generator (lives in Cthulhu, follows gen-ai's pattern). When endpoints change, docs regenerate instead of being hand-edited.

• Covers the 11 public-preview vector database endpoints. Schemas consolidated in definitions.yml (replacing the previous models/ and responses/ dirs).
• Incorporates Add Vector Databases API spec for public preview #1181 review feedback: region examples now tor1, corrected gRPC/HTTP endpoint format, "Weaviate" removed from public descriptions (field name weaviate_version kept as API contract), gRPC casing + "arbitrary" typo fixed.
• Security scopes match the proto's required_permissions; success codes 201/204/200.
• Three new endpoints (fork, list-plans, rotate-credentials) deferred to a follow-up.
• make bundle clean; make lint 0 errors (2 pre-existing pagination param warnings on shared page/per_page, deferred).

Generator PR (Cthulhu): https://github.internal.digitalocean.com/digitalocean/cthulhu/pull/163690
Supersedes #1181.