feat(common-config): show first-run notice dialog when editing providers

Display a one-time informational dialog explaining the Common Config
Snippet feature when users first open the add/edit provider form.
Uses a derived isOpen state from settings to avoid race conditions.
Adds commonConfigConfirmed flag to both TS and Rust settings types.

src-tauri/src/settings.rs

@@ -208,6 +208,9 @@ pub struct AppSettings {
     /// User has confirmed the first-run welcome notice
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub first_run_notice_confirmed: Option<bool>,
+    /// User has confirmed the common config first-run notice
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub common_config_confirmed: Option<bool>,
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub language: Option<String>,
 
@@ -301,6 +304,7 @@ impl Default for AppSettings {
             enable_failover_toggle: false,
             failover_confirmed: None,
             first_run_notice_confirmed: None,
+            common_config_confirmed: None,
             language: None,
             visible_apps: None,
             claude_config_dir: None,