feat(monitoring): Tempo + OTel Collector for tripit tracing, hardened (ADR-0032 Phase 2)

Re-land Phase 2 after the first attempt's two failure modes, both fixed:
- tempo.resources set under the correct single-binary chart key (was OOMKilled on
  the namespace LimitRange default when mis-placed at top level).
- atomic=true + cleanup_on_fail=true on BOTH helm releases — a failed install
  auto-rolls-back instead of leaving a stuck/orphaned release (memory #6479).

Tempo (single-binary, proxmox-lvm 20Gi, 30d) + OTel Collector (contrib; otlp ->
redaction -> batch -> tempo) + Tempo datasource + additive trace_id->Tempo
derivedField on Loki + tripit LOG_FORMAT=json/OTEL_EXPORTER_OTLP_ENDPOINT.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

stacks/tripit/main.tf

@@ -131,6 +131,12 @@ locals {
     # not-yet-visited countries + real UK bank-holiday leave windows + fares).
     # `claude_agent` mode requires images >= the #23 slice (already deployed).
     RESEARCH_PROVIDER = "claude_agent"
+    # Observability (tripit ADR-0032, Phase 2): structured JSON logs (so Loki's
+    # trace_id derivedField links to Tempo) + OTLP trace export to the in-cluster
+    # OTel Collector -> Tempo. Both require images >= the observability slice
+    # (v0.81.0, already live), so they land after that rollout.
+    LOG_FORMAT                  = "json"
+    OTEL_EXPORTER_OTLP_ENDPOINT = "http://otel-collector-opentelemetry-collector.monitoring.svc.cluster.local:4318/v1/traces"
     # Stay cover photos (tripit issue #47, ADR-0017): auto-fetch each picked
     # city's Wikipedia lead image (keyless REST summary API, "City, Country"
     # first), downloaded into the app's STORAGE_DIR (never hotlinked) and