feat: add /bookshelf route and update redirects

- Add /bookshelf route as default page for logged-in users
- Update login and register handlers to redirect to /bookshelf
- Update homepage to auto-redirect to /bookshelf when logged in
- Preserve /dashboard route for backward compatibility
- Update test redirects to use /bookshelf

Changes:
- main.go: Add /bookshelf protected route
- auth.go: Change login/register redirects from /api/dashboard to /bookshelf (2 locations)
- edge_cases_test.go: Update test redirect to /bookshelf
- Maintains backward compatibility with existing /dashboard route

This makes the beautiful bookshelf the default landing page
for all authenticated users while keeping the old dashboard accessible.

internal/handlers/auth.go

@@ -256,7 +256,7 @@ localStorage.setItem('token', '%s');
 localStorage.setItem('refreshToken', '%s');
 localStorage.setItem('user', JSON.stringify(%s));
 document.cookie = 'token=%s; path=/; max-age=3600';
-window.location.href = '/api/dashboard';
+window.location.href = '/bookshelf';
 </script>`, accessToken, refreshToken, fmt.Sprintf(`{"id":"%s","email":"%s","username":"%s"}`, uuid.UUID(user.ID.Bytes).String(), user.Email, user.Username), accessToken)
 		return c.HTML(http.StatusCreated, html)
 	}
@@ -412,7 +412,7 @@ localStorage.setItem('token', '%s');
 localStorage.setItem('refreshToken', '%s');
 localStorage.setItem('user', JSON.stringify(%s));
 document.cookie = 'token=%s; path=/; max-age=3600';
-window.location.href = '/api/dashboard';
+window.location.href = '/bookshelf';
 </script>`, accessToken, refreshToken, fmt.Sprintf(`{"id":"%s","email":"%s","username":"%s","first_name":"%s","last_name":"%s"}`, uuid.UUID(user.ID.Bytes).String(), user.Email, user.Username, user.FirstName.String, user.LastName.String), accessToken)
 		return c.HTML(http.StatusOK, html)
 	}