refactor: migrate all Tauri commands to camelCase parameters

This commit addresses parameter naming inconsistencies caused by Tauri v2's
requirement for camelCase parameter names in IPC commands.

Backend changes (Rust):
- Updated all command parameters from snake_case to camelCase
- Commands affected:
  * provider.rs: providerId (×4), timeoutSecs
  * import_export.rs: filePath (×2), defaultName
  * config.rs: defaultPath
- Added #[allow(non_snake_case)] attributes for camelCase parameters
- Removed unused QueryUsageParams struct

Frontend changes (TypeScript):
- Removed redundant snake_case parameters from all invoke() calls
- Updated API files:
  * usage.ts: removed debug logs, unified to providerId
  * vscode.ts: updated 8 functions (providerId, timeoutSecs, filePath, defaultName)
  * settings.ts: updated 4 functions (defaultPath, filePath, defaultName)
- Ensured all parameters now use camelCase exclusively

Test updates:
- Updated MSW handlers to accept both old and new parameter formats during transition
- Added i18n mock compatibility for tests

Root cause:
The issue stemmed from Tauri v2 strictly requiring camelCase for command
parameters, while the codebase was using snake_case. This caused parameters
like 'provider_id' to not be recognized by the backend, resulting in
"missing providerId parameter" errors.

BREAKING CHANGE: All Tauri command invocations now require camelCase parameters.
Any external tools or scripts calling these commands must be updated accordingly.

Fixes: Usage query always failing with "missing providerId" error
Fixes: Custom endpoint management not receiving provider ID
Fixes: Import/export dialogs not respecting default paths

src-tauri/src/commands/config.rs

@@ -73,9 +73,10 @@ pub async fn open_config_folder(handle: AppHandle, app: String) -> Result<bool,
 #[tauri::command]
 pub async fn pick_directory(
     app: AppHandle,
-    default_path: Option<String>,
+    #[allow(non_snake_case)]
+    defaultPath: Option<String>,
 ) -> Result<Option<String>, String> {
-    let initial = default_path
+    let initial = defaultPath
         .map(|p| p.trim().to_string())
         .filter(|p| !p.is_empty());