fix(auth): tighten API URL match, add Retry-After header, and add missing tests

- frontend/hooks.server.ts: replace request.url.includes('/api/') with
  new URL(request.url).pathname.startsWith('/api/') so a page named
  /my-api/something cannot accidentally match the API gate
- DomainException: add optional retryAfterSeconds field and a new
  tooManyRequests() factory overload that carries the value
- LoginRateLimiter: pass windowMinutes * 60 as retryAfterSeconds when
  throwing TOO_MANY_LOGIN_ATTEMPTS (RFC 6585 §4 SHOULD)
- GlobalExceptionHandler: emit Retry-After header when retryAfterSeconds
  is set on a DomainException
- RateLimitInterceptor: emit Retry-After: 60 on 429 responses (1-min
  window matches the existing MAX_REQUESTS_PER_MINUTE logic)
- LoginRateLimiterTest: assert retryAfterSeconds equals window duration
- RateLimitInterceptorTest: assert Retry-After header is set on 429
- JdbcSessionRevocationAdapterIntegrationTest: new @SpringBootTest +
  Testcontainers test verifying revokeAll deletes all spring_session rows
  and revokeOther leaves the current session intact

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

backend/src/main/java/org/raddatz/familienarchiv/auth/LoginRateLimiter.java

@@ -42,16 +42,17 @@ public class LoginRateLimiter {
     // For the current single-VPS setup this is the correct, simplest implementation.
 
     public void checkAndConsume(String ip, String email) {
+        long retryAfterSeconds = windowMinutes * 60L;
         String key = ip + ":" + email.toLowerCase(Locale.ROOT);
         if (!byIpEmail.get(key).tryConsume(1)) {
             throw DomainException.tooManyRequests(ErrorCode.TOO_MANY_LOGIN_ATTEMPTS,
-                    "Too many login attempts from " + ip);
+                    "Too many login attempts from " + ip, retryAfterSeconds);
         }
         if (!byIp.get(ip).tryConsume(1)) {
             // Refund the ipEmail token so IP-level blocking does not erode the per-email quota.
             byIpEmail.get(key).addTokens(1);
             throw DomainException.tooManyRequests(ErrorCode.TOO_MANY_LOGIN_ATTEMPTS,
-                    "Too many login attempts from " + ip);
+                    "Too many login attempts from " + ip, retryAfterSeconds);
         }
     }
 

backend/src/main/java/org/raddatz/familienarchiv/config/RateLimitInterceptor.java

@@ -28,6 +28,7 @@ public class RateLimitInterceptor implements HandlerInterceptor {
         AtomicInteger count = requestCounts.get(ip, k -> new AtomicInteger(0));
         if (count.incrementAndGet() > MAX_REQUESTS_PER_MINUTE) {
             response.setStatus(HttpStatus.TOO_MANY_REQUESTS.value());
+            response.setHeader("Retry-After", "60");
             response.getWriter().write("{\"code\":\"RATE_LIMIT_EXCEEDED\",\"message\":\"Too many requests\"}");
             return false;
         }

backend/src/main/java/org/raddatz/familienarchiv/exception/DomainException.java

@@ -10,11 +10,21 @@ public class DomainException extends RuntimeException {
 
     private final ErrorCode code;
     private final HttpStatus status;
+    /** Seconds until the rate-limit window resets; {@code null} when not applicable. */
+    private final Long retryAfterSeconds;
 
     public DomainException(ErrorCode code, HttpStatus status, String developerMessage) {
         super(developerMessage);
         this.code = code;
         this.status = status;
+        this.retryAfterSeconds = null;
+    }
+
+    private DomainException(ErrorCode code, HttpStatus status, String developerMessage, Long retryAfterSeconds) {
+        super(developerMessage);
+        this.code = code;
+        this.status = status;
+        this.retryAfterSeconds = retryAfterSeconds;
     }
 
     public ErrorCode getCode() {
@@ -25,6 +35,11 @@ public class DomainException extends RuntimeException {
         return status;
     }
 
+    /** Returns the {@code Retry-After} value in seconds, or {@code null} if not set. */
+    public Long getRetryAfterSeconds() {
+        return retryAfterSeconds;
+    }
+
     // --- Static factories for common cases ---
 
     public static DomainException notFound(ErrorCode code, String message) {
@@ -59,4 +74,8 @@ public class DomainException extends RuntimeException {
     public static DomainException tooManyRequests(ErrorCode code, String message) {
         return new DomainException(code, HttpStatus.TOO_MANY_REQUESTS, message);
     }
+
+    public static DomainException tooManyRequests(ErrorCode code, String message, long retryAfterSeconds) {
+        return new DomainException(code, HttpStatus.TOO_MANY_REQUESTS, message, retryAfterSeconds);
+    }
 }

backend/src/main/java/org/raddatz/familienarchiv/exception/GlobalExceptionHandler.java

@@ -23,9 +23,11 @@ public class GlobalExceptionHandler {
 
     @ExceptionHandler(DomainException.class)
     public ResponseEntity<ErrorResponse> handleDomain(DomainException ex) {
-        return ResponseEntity
-            .status(ex.getStatus())
-            .body(new ErrorResponse(ex.getCode(), ex.getMessage()));
+        var builder = ResponseEntity.status(ex.getStatus());
+        if (ex.getRetryAfterSeconds() != null) {
+            builder = builder.header("Retry-After", String.valueOf(ex.getRetryAfterSeconds()));
+        }
+        return builder.body(new ErrorResponse(ex.getCode(), ex.getMessage()));
     }
 
     @ExceptionHandler(MethodArgumentNotValidException.class)