Update OpenAPI spec to use v0.1 endpoints

[tadasant]

Prepared by Claude Code, reviewed by me.

[!IMPORTANT] This PR depends on #803 and must be merged after it. PR #803 decouples the server.schema.json versioning from openapi.yaml by using a draft URL scheme. Until #803 is merged, CI will fail because the schema generation tool expects server.schema.json to be regenerated from openapi.yaml, but this PR intentionally does not modify server.schema.json to avoid conflicts. After #803 merges, a rebase will resolve the CI failure.

Summary

• Update all API endpoint paths from /v0/ to /v0.1/ in the OpenAPI spec
• Bump OpenAPI spec version from 2025-10-17 to 2025-12-01 (in $id and info.version)

Rationale

This ensures sub-registries implementing the spec are adhering to the stable v0.1 version rather than the unstable v0. The API freeze (v0.1) provides stability guarantees that sub-registries need.

Test plan

• [x] Changes are limited to openapi.yaml only
• [ ] CI passes (will pass after rebasing on #803)

🤖 Generated with Claude Code