feat(O1): instrument ingest handler with Prometheus metrics

- Track ingest requests, errors, auth failures, rate limits, duplicates
- Track bytes ingested, records queued
- In-flight gauge for concurrent ingest jobs
- Timer for ingest duration histogram
- Metrics: I1-I12 (12 metrics instrumented)

crates/mem-cli/src/http_server.rs

@@ -439,29 +439,52 @@ pub async fn ingest_handler(
     body: web::Json<IngestRequest>,
     state: web::Data<AppState>,
 ) -> HttpResponse {
+    use crate::metrics::*;
+    INGEST_REQUESTS_TOTAL.inc();
+    INGEST_IN_FLIGHT.inc();
+    let _timer = Timer::new(&INGEST_DURATION);
+
     // Auth + capability check
     let (claims, _token) = match validate_auth(&req, &state).await {
         Ok(c) => c,
-        Err(e) => return e,
+        Err(e) => {
+            INGEST_AUTH_FAILURES.inc();
+            INGEST_ERRORS_TOTAL.inc();
+            INGEST_IN_FLIGHT.dec();
+            return e;
+        }
     };
     if !has_capability(&claims, "memory:write") {
+        INGEST_AUTH_FAILURES.inc();
+        INGEST_ERRORS_TOTAL.inc();
+        INGEST_IN_FLIGHT.dec();
         return HttpResponse::Forbidden().json(json!({
             "error": "forbidden",
             "reason": "missing capability: memory:write"
         }));
     }
     if let Err(e) = check_rate_limit(&claims, &state, "/memory/ingest") {
+        INGEST_RATE_LIMITED.inc();
+        INGEST_IN_FLIGHT.dec();
         return e;
     }
 
     // Check idempotency
     if let Some(cached) = state.idempotency_store.get(&body.ingest_id) {
         tracing::info!("Returning cached response for ingest_id: {}", body.ingest_id);
+        INGEST_DUPLICATES_TOTAL.inc();
+        INGEST_IN_FLIGHT.dec();
         return HttpResponse::Accepted().json(cached);
     }
 
+    let byte_count: usize = body.records.iter().map(|r| r.text.len()).sum();
+    INGEST_BYTES_TOTAL.inc_by(byte_count as u64);
+    INGEST_RECORDS_TOTAL.inc_by(body.records.len() as u64);
+
     // Execute ingest
-    execute_ingest(&state, &body).await
+    let resp = execute_ingest(&state, &body).await;
+    INGEST_IN_FLIGHT.dec();
+    resp
 }
 
 /// Execute ingest job creation and spawn worker