gleam db: insert_book (Create)

[HeyItWorked]

Sub-issue of #9, depends on #9a (shared helpers)

pub fn insert_book(conn, title, author, status) -> Result(Book, AppError)

• INSERT INTO books (title, author, status) VALUES ($1, $2, $3) RETURNING id, title, author, status
• Convert BookStatus to string via status_to_string for the $3 parameter
• Pattern match returned.rows — expect exactly [book], otherwise DatabaseError

[HeyItWorked]

What and why

Takes conn, title, author, status → runs INSERT ... RETURNING → gives back the new Book with its generated id.

The RETURNING clause gets the row back in one round trip (same as Go/TS). status_to_string converts the BookStatus type to the string Postgres expects. use returned <- result.try(...) short-circuits if the query fails. The case returned.rows at the end confirms we got exactly one row — anything else means something unexpected happened.

15 lines of logic — most of it is the pog pipeline.