feat(openapi): add tag changes upload flag

[HugoHSun]

🚥 Resolves CX-2165

🧰 Changes

Adds an --apply-tag-changes flag to rdme openapi upload. When updating an existing API definition, opting in moves existing endpoint pages to the tags declared in the uploaded OAS file. The flag is ignored when creating a definition, and cross-category moves are not affected.

Related backend changes:

• ReadMe API support
• Gitto tag processing

🧬 QA & Testing

• Update an existing API definition with an operation moved to another tag and pass --apply-tag-changes. Confirm its endpoint page moves to the new tag.
• Repeat without the flag and confirm the existing endpoint page placement is unchanged.
• Create a new API definition with the flag and confirm creation still succeeds normally.

[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge with no concrete changed-code defect identified.

The new option is parsed by the real command path, included only on existing-definition PUT requests, omitted from creation requests as intended, and covered by payload assertions and generated documentation.

_{Reviews (1): Last reviewed commit: "Merge branch 'next' into hugo/cx-2165-ch..." | Re-trigger Greptile}

[HugoHSun]

Closing this in favour of the OAS extension