feat: add ability to configure the agent (also theme switcher) (#3)

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### Tests

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Reviewed-on: #3
Co-authored-by: Naomi Carrigan <commits@nhcarrigan.com>
Co-committed-by: Naomi Carrigan <commits@nhcarrigan.com>

src-tauri/src/config.rs

@@ -0,0 +1,96 @@
+use serde::{Deserialize, Serialize};
+
+#[derive(Debug, Clone, Serialize, Deserialize, Default)]
+pub struct ClaudeStartOptions {
+    #[serde(default)]
+    pub working_dir: String,
+
+    #[serde(default)]
+    pub model: Option<String>,
+
+    #[serde(default)]
+    pub api_key: Option<String>,
+
+    #[serde(default)]
+    pub custom_instructions: Option<String>,
+
+    #[serde(default)]
+    pub mcp_servers_json: Option<String>,
+
+    #[serde(default)]
+    pub allowed_tools: Vec<String>,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize, Default)]
+pub struct HikariConfig {
+    #[serde(default)]
+    pub model: Option<String>,
+
+    #[serde(default)]
+    pub api_key: Option<String>,
+
+    #[serde(default)]
+    pub custom_instructions: Option<String>,
+
+    #[serde(default)]
+    pub mcp_servers_json: Option<String>,
+
+    #[serde(default)]
+    pub auto_granted_tools: Vec<String>,
+
+    #[serde(default)]
+    pub theme: Theme,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize, Default, PartialEq)]
+#[serde(rename_all = "lowercase")]
+pub enum Theme {
+    #[default]
+    Dark,
+    Light,
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_default_config() {
+        let config = HikariConfig::default();
+        assert!(config.model.is_none());
+        assert!(config.api_key.is_none());
+        assert!(config.custom_instructions.is_none());
+        assert!(config.mcp_servers_json.is_none());
+        assert!(config.auto_granted_tools.is_empty());
+        assert_eq!(config.theme, Theme::Dark);
+    }
+
+    #[test]
+    fn test_config_serialization() {
+        let config = HikariConfig {
+            model: Some("claude-sonnet-4-20250514".to_string()),
+            api_key: None,
+            custom_instructions: Some("Be helpful".to_string()),
+            mcp_servers_json: None,
+            auto_granted_tools: vec!["Read".to_string(), "Glob".to_string()],
+            theme: Theme::Light,
+        };
+
+        let json = serde_json::to_string(&config).unwrap();
+        let deserialized: HikariConfig = serde_json::from_str(&json).unwrap();
+
+        assert_eq!(deserialized.model, config.model);
+        assert_eq!(deserialized.custom_instructions, config.custom_instructions);
+        assert_eq!(deserialized.auto_granted_tools, config.auto_granted_tools);
+        assert_eq!(deserialized.theme, Theme::Light);
+    }
+
+    #[test]
+    fn test_theme_serialization() {
+        let dark = Theme::Dark;
+        let light = Theme::Light;
+
+        assert_eq!(serde_json::to_string(&dark).unwrap(), "\"dark\"");
+        assert_eq!(serde_json::to_string(&light).unwrap(), "\"light\"");
+    }
+}