chore(telemetry): update Loki to 3.7.6 and refresh version references

Bumps the Loki pin this branch introduced, and updates the two docs that
name the version so they do not drift from the compose file:
  - OpenTelemetryPlan/09-data-collection-reference.md (log backend section)
  - OpenTelemetryPlan/Phase8_taskList.md (compose snippet)

The service runs the config bundled in the image rather than one from this
repo; `-verify-config` reports "config is valid" under 3.7.6, and native OTLP
ingestion at /otlp is unchanged across 3.4 -> 3.7.

OpenTelemetryPlan/09-data-collection-reference.md

@@ -967,7 +967,7 @@ Bidirectional linking between logs and traces is configured via Grafana datasour
 
 ### Loki Backend
 
-Grafana Loki (v3.4.2) serves as the log storage backend. It receives log entries from the OTel Collector's `otlphttp/loki` exporter via the native OTLP endpoint at `http://loki:3100/otlp`.
+Grafana Loki (v3.7.6) serves as the log storage backend. It receives log entries from the OTel Collector's `otlphttp/loki` exporter via the native OTLP endpoint at `http://loki:3100/otlp`.
 
 ### LogQL Query Examples
 

OpenTelemetryPlan/Phase8_taskList.md

@@ -76,7 +76,7 @@
   - Add Loki service:
     ```yaml
     loki:
-      image: grafana/loki:3.4.2
+      image: grafana/loki:3.7.6
       ports:
         - "3100:3100"
       command: -config.file=/etc/loki/local-config.yaml

docker/telemetry/docker-compose.yml

@@ -69,7 +69,7 @@ services:
   # Collector exports via otlphttp to Loki's /otlp endpoint.
   # Query logs via Grafana Explore -> Loki at http://localhost:3000.
   loki:
-    image: grafana/loki:3.4.2
+    image: grafana/loki:3.7.6
     ports:
       - "3100:3100"
     command: -config.file=/etc/loki/local-config.yaml