feat(gemini): implement function calling, generationConfig, and update models

- Implement function calling support (functionDeclarations, functionResponse)
- Add functionCall SSE parsing and empty stream retry support
- Add generationConfig (temperature, maxOutputTokens)
- Add thinkingConfig for Gemini 3 and thinking models
- Add toolConfig (functionCallingConfig.mode)
- Fix .expect() panics with .ok_or_else()
- Restrict oauth credentials file permissions to 0600
- Update docs and FEATURE_PARITY.md
- Update wizard to current Gemini 3.1 and 2.5 models

src/config/llm.rs

@@ -378,9 +378,8 @@ impl LlmConfig {
             let credentials_path = optional_env("GEMINI_CREDENTIALS_PATH")?
                 .map(PathBuf::from)
                 .unwrap_or_else(|| {
-                    crate::bootstrap::ironclaw_base_dir()
-                        .parent() // ~/.ironclaw -> ~/
-                        .expect("ironclaw_base_dir has no parent")
+                    dirs::home_dir()
+                        .unwrap_or_else(|| PathBuf::from("/tmp"))
                         .join(".gemini")
                         .join("oauth_creds.json")
                 });