Fix/project embedding transactions

[AmzBG]

Description

• Generate project AI embeddings before opening Prisma interactive transactions.
• Keep project creation, GitHub import, project updates, and vector persistence atomic while preventing AI latency from exhausting Prisma's five-second transaction timeout.
• Add regression coverage for all three project-writing workflows.

Link to issue or ticket

N/A

Steps to QA

1. Run npm test --workspace=api -- --runInBand.
2. Run npx turbo run lint.
3. Run npx turbo run check-types.
4. Run npx turbo run build.
5. Edit a project in an environment where embedding generation takes longer than five seconds.
6. Confirm the project update succeeds without Prisma error P2028 and its embedding is persisted.

Screenshots

N/A