Validate profile chunks and summary on save

[exyw]

What this PR does

• Adds safety + relevance validation when saving profile chunks
• Adds validation when saving the profile summary
• Prevents nonsensical or unsafe text from being saved
• Refactors validation API to remove unused fullName input

Notes

• Validation is intentionally loose to minimise false rejections
• Category matching is only enforced for chunks (not summaries)
• Summary and chunks share the same validation endpoint

Testing

• Edited summary and chunk content
• Verified unsafe / irrelevant text is blocked
• Verified valid content saves successfully