Surface useful, actionable errors in the CLI using `dry/usefulerror`

Problem

CLI errors are often raw gRPC/internal messages that don't help users (or agents) understand what went wrong or how to fix it. Example from query exec:

Error: cloudquery: query: rpc error: code = Internal desc = server closed the stream without sending trailers

This tells the user nothing actionable.

Proposal

Adopt usefulerror from safedep/dry across the CLI so errors carry a human message, help text, and a reference URL instead of leaking transport-level detail.

dry/usefulerror already ships gRPC converters for the standard codes, so most of the mapping comes for free — we render its fields at the CLI's top-level error boundary and add CLI-specific mappings only where the generic message isn't enough.

Docs

Add a troubleshooting page on docs.safedep.io keyed by error code, and link each error's reference URL to the relevant entry. Beyond helping users, this is especially useful for coding agents: when a command fails, an agent can look up the error code and apply the documented fix on its own, instead of the user having to stop, debug, or hunt for a workaround.

Outcome

Errors become self-explanatory and greppable by code, with a doc link for deeper guidance.

Start with the query exec error path and the CLI's top-level error boundary, then review how dry/usefulerror maps standard gRPC codes. Add CLI-specific mappings where needed, render human messages, help text, and reference URLs, and add a docs.safedep.io troubleshooting page keyed by error code with linked guidance.