* refactor: Use more precise terminology in API server logs and error messages
This commit refactors several log and error messages to use more accurate and consistent terminology.
- Replaced "backend servers" and "backend model servers" with "models" or "sessions" to better reflect the service's internal structure.
- Changed "Proxy server" to "Jan API server" to more accurately describe the server's function.
- Removed a redundant debug log message.
These changes are cosmetic and improve the readability and consistency of the logging output.
* Update src-tauri/src/core/server.rs
Co-authored-by: ellipsis-dev[bot] <65095814+ellipsis-dev[bot]@users.noreply.github.com>
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Co-authored-by: ellipsis-dev[bot] <65095814+ellipsis-dev[bot]@users.noreply.github.com>