go: add PATCH /api/v1/users/me user settings update (#15297)

### What problem does this PR solve?

- Add Go implementation parity for `PATCH /api/v1/users/me`.

- This updates the Go user settings endpoint to match the Python
behavior for updating the current user's profile settings.

### Changes

- Route `PATCH /api/v1/users/me` through the authenticated current user
from middleware.
- Add `password` and `new_password` support to `UpdateSettingsRequest`.
- Prevent `email` from being updated through this endpoint, matching the
Python blacklist behavior.
  - Support updating:
    - `nickname`
    - `avatar`
    - `language`
    - `color_schema`
    - `timezone`
    - `password`
  - Align password handling with Python:
    - invalid plaintext password payload returns `CodeExceptionError`
    - wrong old password returns `Password error!`
- successful update returns `{ code: 0, data: true, message: "success"
}`

### Test

Tested manually with Python and Go backends using the same request
bodies:

  - `PATCH /api/v1/users/me` with nickname/timezone update
- plaintext password payload returns Python-compatible `Incorrect
padding`
  - wrong old password returns `Password error!`