Add end to end type safety to board feed queries

[essential-randomness]

We want to test our end to end typesafety flow by adding it to a new endpoint. The chosen candidate is /feeds/boards/{board_id}.

• [x] Create zod type definitions for the "DbActivitySomethingType", which is used to standardize the return type of DB feed queries.
• [x] Generate typescript definition from the OpenAPI types of the /feeds/boards/{board_id} endpoint.
• [x] Swap typescript definitions with new types and check for any discrepancies
• [ ] Add typescript definitions to the frontend and type safe the corresponding queries.

[Reptapog]

all relevant types have been converted to or have Zod equivalents.

board feed still needs to return results parsed by Zod (ref), can confirm that there are some tests that return unexpected results that will need to be looked at and fixed

nothing has been touched at all on the front end yet