[FEATURE] Add distributed tracing with Micrometer and Zipkin TransactionMs

[abengl]

Description
Instrument the transfer flow with distributed tracing so a single transfer request can be visualized as a full trace spanning TransactionMs and AccountMs, with timing at each hop visible in Zipkin UI.

Tasks

• Add micrometer-tracing-bridge-brave and zipkin-reporter-brave dependencies to TransactionMs, AccountMs, and CustomerMs
• Configure management.tracing.sampling.probability=1.0 in dev properties for all services
• Add Zipkin as a service in docker-compose.yml on port 9411
• Verify that WebClient calls automatically propagate trace context (B3 headers) — confirm with a test transfer that both TransactionMs and AccountMs spans appear under the same trace in Zipkin UI
• Add traceId and spanId to the MDC configuration from the previous issue so they appear in structured log output alongside the correlationId
• For the Generator, instrument the runGeneration flow so each generation run produces a parent span with child spans per customer creation batch

Acceptance Criteria

• Zipkin UI at http://localhost:9411 shows traces after a POST /api/v1/transactions/transfer
• The trace shows at minimum two spans: one for TransactionMs and one for the outgoing call to AccountMs
• traceId appears in structured log output and matches the trace visible in Zipkin
• Sampling is configurable via management.tracing.sampling.probability without code changes
• Docker Compose brings up Zipkin alongside the existing services with no manual setup required