✨ feat: integrate configurable rules path throughout CLI

- Make parse_config_root() public for reuse in main.rs
- Add get_rules_path() helper to extract and resolve rules path from config
- Update main CLI to use configured rules path for default rule execution
- Add run_with_rules_path() method to RulesCli for custom path support
- Update all unit tests to include rules_dir field
- Rules path now supports h:, c:, r: prefixes throughout the application

src/cli/rules_cli.rs

@@ -263,7 +263,21 @@ impl RulesCli {
     /// - **Error isolation**: Subcommand errors don't affect rule loading
     /// - **State preservation**: Configuration errors don't corrupt existing rules
     pub async fn run(&self, client: &mut GmailClient) -> Result<()> {
-        let rules = get_rules()?;
+        self.run_with_rules_path(client, None).await
+    }
+
+    /// Executes the rules command with an optional custom rules path.
+    ///
+    /// # Arguments
+    ///
+    /// * `client` - Mutable Gmail client for API operations
+    /// * `rules_path` - Optional path to rules file
+    pub async fn run_with_rules_path(
+        &self,
+        client: &mut GmailClient,
+        rules_path: Option<&Path>,
+    ) -> Result<()> {
+        let rules = get_rules_from(rules_path)?;
 
         match &self.sub_command {
             SubCmds::Config(config_cli) => config_cli.run(rules),