fix: replace flyout profile card with logout slider, i18n auth errors

- Replace static account card in mobile flyout with swipe-to-logout widget
- Remove redundant logout button from flyout bottom
- Make LogoutButton full-width via class prop and dynamic maxSlide
- Extract clean GraphQL error messages instead of raw JSON in all auth forms
- Add i18n keys for known backend errors (invalid credentials, email taken, invalid token)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/frontend/src/routes/login/+page.svelte

@@ -32,7 +32,8 @@
       await login(email, password);
       goto("/videos", { invalidateAll: true });
     } catch (err: any) {
-      error = err.message;
+      const raw = err.response?.errors?.[0]?.message ?? err.message;
+      error = raw === "Invalid credentials" ? $_("auth.login.error_invalid_credentials") : raw;
       isError = true;
     } finally {
       isLoading = false;

packages/frontend/src/routes/me/+page.svelte

@@ -87,7 +87,7 @@
       toast.success($_("me.settings.toast_update"));
       invalidateAll();
     } catch (err: any) {
-      profileError = err.message;
+      profileError = err.response?.errors?.[0]?.message ?? err.message;
       isProfileError = true;
     } finally {
       isProfileLoading = false;
@@ -111,7 +111,7 @@
       invalidateAll();
       password = confirmPassword = "";
     } catch (err: any) {
-      securityError = err.message;
+      securityError = err.response?.errors?.[0]?.message ?? err.message;
       isSecurityError = true;
     } finally {
       isSecurityLoading = false;

packages/frontend/src/routes/password/+page.svelte

@@ -31,7 +31,7 @@
       toast.success($_("auth.password_request.toast_request", { values: { email } }));
       goto("/login");
     } catch (err: any) {
-      error = err.message;
+      error = err.response?.errors?.[0]?.message ?? err.message;
       isError = true;
     } finally {
       isLoading = false;

packages/frontend/src/routes/password/reset/+page.svelte

@@ -40,7 +40,9 @@
       toast.success($_("auth.password_reset.toast_reset"));
       goto("/login");
     } catch (err: any) {
-      error = err.message;
+      const raw = err.response?.errors?.[0]?.message ?? err.message;
+      const tokenErrors = ["Invalid or expired reset token", "Reset token expired"];
+      error = tokenErrors.includes(raw) ? $_("auth.password_reset.error_invalid_token") : raw;
       isError = true;
     } finally {
       isLoading = false;

packages/frontend/src/routes/signup/+page.svelte

@@ -48,7 +48,8 @@
       toast.success($_("auth.signup.toast_register", { values: { email } }));
       goto("/login");
     } catch (err: any) {
-      error = err.message;
+      const raw = err.response?.errors?.[0]?.message ?? err.message;
+      error = raw === "Email already registered" ? $_("auth.signup.error_email_taken") : raw;
       isError = true;
     } finally {
       isLoading = false;