Errors: Error codes and errors guide

### What should be done?

Let's introduce error codes to all errors, and publish an error guide, which documents possible common scenarios where a particular error can occur.

### How should it be done?

See "What".
Additional task, create a process for maintaining this error guide (DevRel?), and what support can the Engineering give (ie, if a new error is introduced, it should be documented what can be causing it).

### When is this task done?

When all errors have error codes and a errors guide exists to reference them and help debug.

### Additional context

_No response_

First, locate all error definitions in the codebase, likely in error-handling modules or classes. Assign unique error codes to each. Then, create an errors guide document that lists each code, describes common scenarios, and outlines a maintenance process for future errors. Check if there are existing error tests to understand the error structure.

索引モデルが issue の本文から書いたものです。