Knowledge Base: Organize data by project

[kartpop]

Is your feature request related to a problem?
All knowledge base endpoints currently use a single bucket, making it difficult to perform a clean data flush for NGOs, resulting in offboarding issues.

Describe the solution you'd like

• Organize data into per-project-ID folders within the same bucket (following the audio setup).
• Implement a migration script for existing documents and a legacy fallback option in the code (check top level, then project level).
• Conduct testing on staging first.
• Defer the bring-your-own-bucket/credentials aspect until TAP.

Priority

• P2, September in-person ops/infra sprint.

Original issue

Context

For knowledge base enpoints, everything currently lands in a single bucket. If an NGO uses the product for two years and then requests a full data flush, that's very hard to honour cleanly — an offboarding liability.

Fix

• Same bucket, per-project-ID folders (audio already does this; documents may not).
• Provide a migration script for existing documents and a legacy fallback in code (check top level, then project level).
• Test on staging first.
• The bring-your-own-bucket/credentials half of this is deferred until TAP.

Priority

• P2, September in-person ops/infra sprint.