feat(auth): wire up refresh token endpoint and auto-refresh

- Add POST /api/refresh-token endpoint to router
- Auth store now calls refreshTokenIfNeeded on init and every hour
- Token refreshes automatically when within 2 weeks of expiry

frontend/src/lib/stores/auth.svelte.ts

@@ -32,6 +32,12 @@ class AuthStore {
 	constructor() {
 		if (browser) {
 			this.initializeAuth();
+			// Check token refresh every hour
+			setInterval(() => {
+				if (this.token) {
+					this.refreshTokenIfNeeded();
+				}
+			}, 60 * 60 * 1000);
 		}
 	}
 
@@ -70,6 +76,8 @@ class AuthStore {
 					lastName: ''
 				};
 				this.fetchUserProfile();
+				// Check if token needs refresh
+				this.refreshTokenIfNeeded();
 			} else {
 				this.clearAuth();
 			}