Observability: Initial instrumentation

## Description

Add OTel instrumentation to the tenant-ui (Node.js/Express) component. The ACA-Py plugin (`traction_innkeeper`) requires no separate code changes — it runs inside the same ACA-Py process and inherits all instrumentation from the acapy-agent OTel work.

## Requirements

- Add `@opentelemetry/sdk-node`, `@opentelemetry/auto-instrumentations-node`, `@opentelemetry/sdk-metrics`, `@opentelemetry/exporter-trace-otlp-http`, `@opentelemetry/exporter-metrics-otlp-http` to `tenant-ui` dependencies
- Create `src/tracing.ts` with `NodeSDK` configured with both trace and metric exporters using the HTTP/protobuf exporters (port 4318) — do **not** use gRPC exporters
- Import as the first line of `src/index.ts` before Express initializes

## Acceptance Criteria

- [ ] tenant-ui HTTP spans visible in Tempo
- [ ] HTTP RED metrics from tenant-ui appear in Mimir
- [ ] No regression in existing test suite

Start by reviewing the tenant-ui dependency manifest and the startup flow in src/index.ts, then inspect the requested src/tracing.ts entry point and HTTP/protobuf exporter requirements. Run the existing test suite and verify that tenant-ui spans reach Tempo and RED metrics appear in Mimir without regressions.

Written by the indexing model from the issue text.