fix: address code review issues in gemini-cli OAuth integration

- Add cache_read_input_tokens/cache_creation_input_tokens fields (value 0)
- Implement manual Debug for OAuthCredential to redact tokens
- Fix hardcoded /tmp: use GeminiOauthConfig::default_credentials_path()
- Replace emoji output with plain text markers
- Propagate Client::builder() errors instead of silent fallback
- Use tokio::fs for all file I/O in CredentialManager (was std::fs)
- Use if let Some(ref pid) to avoid consuming credential.project_id
- Extract uses_cloud_code_api() helper; route by major version (gemini-2+)
- Concatenate multiple system messages into systemInstruction
- Include functionCall parts in assistant message conversion
- Add 401 retry loop with allow_retry flag for auth failures
- Remove biased from tokio::select! in OAuth callback handler
- Remove hardcoded context_length 1M; vary by model family
- Change GOOG_API_CLIENT from Node.js spoof to gl-rust/1.0.0
- Implement list_models() with static model list
- Move create_gemini_oauth_provider() before test module (clippy)
- Fix 9 additional clippy warnings (collapsible_if, map_or, needless_borrow)
- Run cargo fmt

src/config/llm.rs

@@ -46,8 +46,6 @@ impl std::str::FromStr for CacheRetention {
                 "invalid cache retention '{}', expected one of: none, short, long",
                 s
             )),
-                s
-            )),
         }
     }
 }
@@ -203,6 +201,7 @@ impl LlmConfig {
             },
             provider: None,
             bedrock: None,
+            gemini_oauth: None,
             request_timeout_secs: 120,
         }
     }
@@ -334,16 +333,11 @@ impl LlmConfig {
 
         let request_timeout_secs = parse_optional_env("LLM_REQUEST_TIMEOUT_SECS", 120)?;
 
-        let gemini_oauth = if backend == LlmBackend::GeminiOauth {
+        let gemini_oauth = if backend_lower == "gemini_oauth" || backend_lower == "gemini-oauth" {
             let model = Self::resolve_model("GEMINI_MODEL", settings, "gemini-2.5-flash")?;
             let credentials_path = optional_env("GEMINI_CREDENTIALS_PATH")?
                 .map(PathBuf::from)
-                .unwrap_or_else(|| {
-                    dirs::home_dir()
-                        .unwrap_or_else(|| PathBuf::from("/tmp"))
-                        .join(".gemini")
-                        .join("oauth_creds.json")
-                });
+                .unwrap_or_else(GeminiOauthConfig::default_credentials_path);
             Some(GeminiOauthConfig {
                 model,
                 credentials_path,
@@ -504,7 +498,6 @@ impl LlmConfig {
             model,
             extra_headers,
             oauth_token,
->>>>>>> origin/main
         })
     }
 }