fix(metrics): MetricsFlushScheduler honour ingestion config flush interval

The @Scheduled placeholder read ${ingestion.flush-interval-ms:1000}
(unprefixed) but IngestionConfig binds cameleer.server.ingestion.* —
YAML tuning of the metrics flush interval was silently ignored and the
scheduler fell back to the 1s default in every environment.

Corrected to ${cameleer.server.ingestion.flush-interval-ms:1000}.

(The initial attempt to bind via SpEL #{@ingestionConfig.flushIntervalMs}
failed because beans registered via @EnableConfigurationProperties use a
compound bean name "<prefix>-<FQN>", not the simple camelCase form. The
property-placeholder path is sufficient — IngestionConfig still owns
the Java-side default.)

BackpressureIT: drops the obsolete workaround property
`ingestion.flush-interval-ms=60000`; the single prefixed override now
controls both buffer config and flush cadence.

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

cameleer-server-app/src/main/java/com/cameleer/server/app/ingestion/MetricsFlushScheduler.java

@@ -30,7 +30,7 @@ public class MetricsFlushScheduler implements SmartLifecycle {
         this.batchSize = config.getBatchSize();
     }
 
-    @Scheduled(fixedDelayString = "${ingestion.flush-interval-ms:1000}")
+    @Scheduled(fixedDelayString = "${cameleer.server.ingestion.flush-interval-ms:1000}")
     public void flush() {
         try {
             List<MetricsSnapshot> batch = metricsBuffer.drain(batchSize);

cameleer-server-app/src/test/java/com/cameleer/server/app/controller/BackpressureIT.java

@@ -23,16 +23,12 @@ import static org.assertj.core.api.Assertions.assertThat;
  */
 @TestPropertySource(properties = {
         // Property keys must match the IngestionConfig @ConfigurationProperties
-        // prefix (cameleer.server.ingestion) exactly — the old "ingestion.*"
-        // form was silently ignored and the metrics buffer stayed at its
-        // default of 50_000, which made the 503 overflow scenario unreachable.
+        // prefix (cameleer.server.ingestion). MetricsFlushScheduler now binds
+        // its flush interval via SpEL on IngestionConfig, so a single override
+        // controls both the buffer config and the flush cadence.
         "cameleer.server.ingestion.buffercapacity=5",
         "cameleer.server.ingestion.batchsize=5",
-        "cameleer.server.ingestion.flushintervalms=60000",
-        // MetricsFlushScheduler's @Scheduled reads ingestion.flush-interval-ms
-        // (a separate key) — override both so the test doesn't race against
-        // the default 1s flush during the fill-then-overflow scenario.
-        "ingestion.flush-interval-ms=60000"
+        "cameleer.server.ingestion.flushintervalms=60000"
 })
 class BackpressureIT extends AbstractPostgresIT {