Decouple connections ⇄ databases: move resource resolvers into the client/ layer

[pthurlow]

Background

The module-layout refactor #200 reorganized src/ into client/, commands/. That work surfaced lateral dependencies between command modules databases/connections.

This cycle dates to the managed-database feature work (d898d99 feat(databases): attach/detach connection catalogs and the managed-database demo flow)

Problem

commands/connections.rs and commands/databases.rs depend on each other:

From	→ To	Symbols
connections	databases	get_database, try_resolve_database
databases	connections	resolve_connection_id, try_resolve_connection_id

It compiles but you can't read either module in isolation. The cycle exists because connection resolution itself consults managed-database catalog aliases.

Two more lateral deps ride along (lower stakes, same root cause):

• indexes → connections (resolve_connection_id), indexes → databases (list_database_ids, get_database)
• results → query (fetch_arrow_result, print_result)

Proposed approach

The shared functions are resolvers — "given a user-typed name/id, hit the API and return the resource." That's a client/-layer concern, not a command concern. Move them down so commands depend downward on client:: instead of sideways on each other.

1. Introduce client/resources/connections.rs and client/resources/databases.rs.
2. Move the resolvers there — and the model structs they return (Database at commands/databases.rs:254, plus the connection lookup's private Connection/ListResponse). This is the main effort: those models are woven into the owning commands' display code, which must then import them back from client/.
3. With both resolvers as siblings in client/resources/, they can cooperate freely and the command-level cycle disappears.
4. Repoint the ~6 call sites in connections, databases, indexes, results.

Design notes

• Keep the client layer side-effect-free. Mirror the auth → client/credentials split: the pure try_resolve_* (return Result) functions belong in client/; the resolve_* / *_or_exit wrappers that print + std::process::exit are UI — leave thin shims in the command modules or drop them.
• fetch_arrow_result (API fetch) → client/; print_result (rendering) → stays presentation (commands/query or output/).

Acceptance criteria

• No crate::commands::X reference appears inside another commands/ module for the resolver/model symbols above (except the allowed update→skill).
• grep -rn "crate::commands" src/client/ returns nothing (client never depends on commands).
• connections and databases no longer reference each other.
• cargo test green; cargo clippy no new warnings.