handbook: update the code intel team index
Created by: creachadair
- Add a "Direction" section to the code intel index, to give a higher-level view of the team's purpose.
- Add a contacts & planning section, to give pointers to team documentation.
- Clarify the code intel tech stack (chiefly: Removes mention of LSP).
Please pay particular attention to the wording of the "Direction" section. I believe this is consistent with our previous discussions, but since we haven't previously written these points in the Handbook, I'd like to be sure we are in agreement.