feat(mana-ai): OpenTelemetry tracing + Grafana Tempo backend

Add distributed tracing to the mana-ai background runner so mission
execution can be visualized end-to-end in Grafana.

Instrumentation (services/mana-ai/):
- tracing.ts: OTel provider setup with OTLP/HTTP exporter, withSpan() helper
- tick.ts: tick.planMission span with mission/agent/user attributes
- client.ts: planner.complete span with LLM model, tokens, latency

Infrastructure:
- docker/tempo/tempo.yaml: Grafana Tempo config (OTLP HTTP on 4318)
- docker-compose: tempo service + tempo_data volume + mana-ai env var
- docker/grafana/provisioning/datasources/tempo.yml: auto-provisioned

Trace flow:
  tick.planMission (root span)
    └── planner.complete (child span)
        ├── llm.model = "gpt-4o-mini"
        ├── llm.tokens.total = 1234
        └── llm.response.length = 567

Enable: set OTEL_EXPORTER_OTLP_ENDPOINT=http://localhost:4318
View: Grafana → Explore → Tempo datasource

Also fixes: removed broken @mana/subscriptions workspace ref from arcade.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docker/grafana/provisioning/datasources/tempo.yml

@@ -0,0 +1,20 @@
+apiVersion: 1
+
+datasources:
+  - name: Tempo
+    type: tempo
+    access: proxy
+    url: http://tempo:3200
+    isDefault: false
+    jsonData:
+      httpMethod: GET
+      tracesToLogsV2:
+        datasourceUid: loki
+        spanStartTimeShift: "-1h"
+        spanEndTimeShift: "1h"
+        filterByTraceID: true
+        filterBySpanID: false
+      tracesToMetrics:
+        datasourceUid: prometheus
+        spanStartTimeShift: "-1h"
+        spanEndTimeShift: "1h"

docker/tempo/tempo.yaml

@@ -0,0 +1,29 @@
+stream_over_http_enabled: true
+server:
+  http_listen_port: 3200
+
+distributor:
+  receivers:
+    otlp:
+      protocols:
+        http:
+          endpoint: "0.0.0.0:4318"
+
+storage:
+  trace:
+    backend: local
+    local:
+      path: /var/tempo/traces
+    wal:
+      path: /var/tempo/wal
+
+metrics_generator:
+  storage:
+    path: /var/tempo/metrics
+  traces_storage:
+    path: /var/tempo/traces
+
+overrides:
+  defaults:
+    metrics_generator:
+      processors: []