Pino-to-Axiom log shipping decision and implementation

[ncolesummers]

Summary

Choose and implement the Pino-to-Axiom log shipping path after ADR 0012 selected Axiom for telemetry, while preserving stdout logging and redaction guarantees.

Deliverables

• Compare OTLP logs versus a Pino transport for Loopworks on Vercel.
• Record the decision in docs or an ADR update, including why Vercel Pro-only log drains are not required for the initial path.
• Wire the chosen log shipping path behind src/lib/observability/ without disrupting existing stdout capture.
• Attach active trace context to structured logs where available.
• Document required environment variables and local-development defaults.

Acceptance Criteria

• Focused tests are written first and demonstrate the red state before production code changes.
• The decision is documented with trade-offs, operational constraints, and rollback/fallback behavior.
• Existing redaction coverage still proves tokens, secrets, authorization fields, webhook-sensitive data, and raw prompts are not shipped.
• Logs include active trace identifiers when trace context is available.
• Vercel stdout logging continues to work without Axiom configuration.
• Runtime/configuration changes include bun run build; broad observability changes finish with bun run validate.

Notes

• Do not introduce Axiom-specific SDK usage outside src/lib/observability/.
• Preserve ADR 0003 logging rules and ADR 0012 correlation alignment.
• This issue should not define dashboard or alert thresholds; those are separate follow-ups.

Refs #21
Refs ADR 0012