feat(diagrams): add findLatestContentHashForAppRoute with app-route cache

Agent-scoped lookups miss diagrams from routes whose publishing agents
have been redeployed or removed. The new method resolves by
(applicationId, environment, routeId) + created_at DESC, independent of
the agent registry. An in-memory cache mirrors the existing hashCache
pattern, warm-loaded at startup via argMax.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

cameleer-server-core/src/main/java/com/cameleer/server/core/storage/DiagramStore.java

@@ -17,5 +17,19 @@ public interface DiagramStore {
 
     Optional<String> findContentHashForRouteByAgents(String routeId, List<String> instanceIds);
 
+    /**
+     * Return the most recently stored {@code content_hash} for the given
+     * {@code (applicationId, environment, routeId)} triple, regardless of the
+     * agent instance that produced it.
+     *
+     * <p>Unlike {@link #findContentHashForRoute(String, String)} and
+     * {@link #findContentHashForRouteByAgents(String, List)}, this lookup is
+     * independent of the agent registry — so it keeps working for routes
+     * whose publishing agents have since been redeployed or removed.
+     */
+    Optional<String> findLatestContentHashForAppRoute(String applicationId,
+                                                      String routeId,
+                                                      String environment);
+
     Map<String, String> findProcessorRouteMapping(String applicationId, String environment);
 }

cameleer-server-core/src/test/java/com/cameleer/server/core/ingestion/ChunkAccumulatorTest.java

@@ -23,6 +23,7 @@ class ChunkAccumulatorTest {
         public Optional<com.cameleer.common.graph.RouteGraph> findByContentHash(String h) { return Optional.empty(); }
         public Optional<String> findContentHashForRoute(String r, String a) { return Optional.empty(); }
         public Optional<String> findContentHashForRouteByAgents(String r, List<String> a) { return Optional.empty(); }
+        public Optional<String> findLatestContentHashForAppRoute(String app, String r, String env) { return Optional.empty(); }
         public Map<String, String> findProcessorRouteMapping(String app, String env) { return Map.of(); }
     };