feat(014-full-observability): real distributed tracing + first 5 business metrics

User Story 3: initializes a real OpenTelemetry TracerProvider (previously
inert — getTracer() returned a no-op tracer with nothing ever exported).
Adds ticket.create, ai.escalation, and orchestration.assignment spans
covering both FR-006 cross-module paths, verified via a real, in-memory
test exporter that confirms actual trace/parent-span nesting, not mocked.

Also registers an AsyncLocalStorageContextManager
(@opentelemetry/context-async-hooks) — without one, OTel's context API is
a no-op that doesn't propagate across the await boundaries this feature's
own event-bus subscribers rely on for span nesting; caught by the first
version of the tracing integration test actually failing on real
parent/child assertions, not assumed.

Graceful degradation (FR-007) verified against a real, deliberately
unreachable OTLP endpoint: the SDK's own background export path (what
production actually exercises) never produces an unhandled rejection.

Starts on the 11 named business-health metrics: AI session
resolved/escalated outcomes (session.repository.ts, the single choke
point every branch in session.service.ts funnels through), human-vs-AI
resolution + resolution-time (a new TICKET_UPDATED/RESOLVED subscriber),
escalation rate (a new subscriber on ESCALATION_TRIGGERED, published
unconditionally since 008 but never previously consumed), and recurring
problems (tickets.service.ts's existing problem-creation call site).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

package.json

@@ -54,6 +54,7 @@
     "@fastify/swagger": "^8.14.0",
     "@fastify/swagger-ui": "^3.0.0",
     "@opentelemetry/api": "^1.8.0",
+    "@opentelemetry/context-async-hooks": "^2.11.0",
     "@opentelemetry/exporter-trace-otlp-http": "^0.222.0",
     "@opentelemetry/resources": "^2.11.0",
     "@opentelemetry/sdk-trace-base": "^2.11.0",