feat: notification center toast coordination (PR-4)

- EventToastBridge checks notification_toast_level and notification_mute_categories
- toast-rules.ts: event-to-category/severity mapping functions
- Settings page: notification preferences section (toast level dropdown, mute checkboxes)
- Settings API types extended with notification preference fields
- 17 frontend tests (toast-rules + bridge)
- Preference hierarchy: mute categories → toast level → show/hide

Quality gates: vitest 17 passed, tsc clean, eslint clean

apps/web/src/api/settings.ts

@@ -1,27 +1,33 @@
 import { apiClient } from "./client";
 
 export interface UserConfig {
-  default_editor: string | null;
-  theme: string;
-  git_user_name: string | null;
-  git_user_email: string | null;
-  last_session_id: string | null;
+	default_editor: string | null;
+	theme: string;
+	git_user_name: string | null;
+	git_user_email: string | null;
+	last_session_id: string | null;
+	notification_toast_level?: "all" | "errors" | "none";
+	notification_mute_categories?: string[];
 }
 
 export interface UserConfigUpdate {
-  default_editor?: string | null;
-  theme?: string | null;
-  git_user_name?: string | null;
-  git_user_email?: string | null;
-  last_session_id?: string | null;
+	default_editor?: string | null;
+	theme?: string | null;
+	git_user_name?: string | null;
+	git_user_email?: string | null;
+	last_session_id?: string | null;
+	notification_toast_level?: "all" | "errors" | "none";
+	notification_mute_categories?: string[];
 }
 
 export const getUserConfig = async (): Promise<UserConfig> => {
-  const response = await apiClient.get<UserConfig>("/users/me/config");
-  return response.data;
+	const response = await apiClient.get<UserConfig>("/users/me/config");
+	return response.data;
 };
 
-export const updateUserConfig = async (data: UserConfigUpdate): Promise<UserConfig> => {
-  const response = await apiClient.patch<UserConfig>("/users/me/config", data);
-  return response.data;
+export const updateUserConfig = async (
+	data: UserConfigUpdate,
+): Promise<UserConfig> => {
+	const response = await apiClient.patch<UserConfig>("/users/me/config", data);
+	return response.data;
 };