[Hard] Implement OAuth flow for Vector Search & Embeddings

[keepsloading]

Implementation issue mapping to the Vector Search & Embeddings epic for the Memory repository.

[keepsloading]

Friendly reminder for SSoC26 contributors: When you submit a Pull Request for this issue, please remember to also raise a dummy PR in the Memact/Context repository that references your original PR. This is required for your contribution to be considered for points on the SSoC leaderboard!

[rach-kanc]

@keepsloading Assign it to me 👍🏻

[rach-kanc]

@keepsloading