Licensing: Standardize to AGPL v3

[kartpop]

Is your feature request related to a problem?
The current licensing across Kaapi repositories is inconsistent: the backend is MIT, Guardrails is GPLv3, and the frontend lacks a license. This creates confusion and potential legal issues.

Describe the solution you'd like
Standardize all three repositories to AGPL v3 to align with Glific and Dalgo. Ensure the following changes:

• Relicense backend to AGPL v3.
• Relicense Guardrails to AGPL v3.
• License frontend as AGPL v3.

Original issue

Context

Current state:

• Kaapi backend = MIT
• Guardrails = GPLv3
• Frontend = no license

Decision

Standardize all three repos to AGPL v3, consistent with Glific and Dalgo. Guardrails Hub being MIT is fine (permissive, compatible).

Acceptance criteria

• Backend relicensed to AGPL v3.
• Guardrails relicensed to AGPL v3.
• Frontend licensed as AGPL v3.

@Prajna1999