Deploy Tempo backend and enable OTLP ingestion for future tracing

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Goal
Deploy Tempo as the trace backend and wire it for OTLP ingestion (so Alloy and/or instrumented apps can send traces).

Scope / Tasks

Create Argo CD Application:

argocd/apps/platform/tempo.yml

Use official Grafana Tempo chart

Configure minimal overrides in valuesObject:

Enable OTLP receivers (grpc/http)

Storage mode:

For homelab: choose filesystem or object store if you already have one

If persistence required: Retain storage class

Wire Alloy:

If Alloy is used as the collector, configure Alloy exporter -> Tempo OTLP endpoint

Acceptance Criteria

Tempo is healthy

OTLP endpoint reachable inside cluster

(Optional smoke test) A simple OTLP trace sent from a test pod is visible in Grafana (after Grafana issue)