feat(agent-observatory): ingest OTLP traces and normalize metrics

[jmagar]

Summary

This draft continues Agent Observatory OTLP ingestion on top of the current main.

• AO-044: persist normalized OTLP trace spans idempotently in one transaction with bounded transient-lock retry, DB-bypass validation, and accepted/duplicate/rejected accounting.
• AO-045: mount authenticated protobuf /v1/traces with privacy-aware normalization, an 8 MiB body cap, 5,000-span cap, partial-success semantics, storage-budget handling, and duplicate-safe persistence.
• AO-046: enable the pinned OTLP metrics messages and normalize gauge/sum points into deterministic MetricPointInput records with privacy-aware metadata, exemplars, JSON-safe non-finite values, stream-safe point keys, and preserved point flags.
• Correct metric point identity so unit, aggregation temporality, and monotonicity participate in the key while description remains non-identifying.
• Preserve /v1/logs behavior and keep production OTLP modules below the repository size gate.

Evidence

• AO-046 focused locked normalization suite: 8/8 passed on the current rebased head.
• Full locked OTLP library regression: 90/90 passed on the current rebased head.
• Exact cargo clippy --all-targets --all-features --locked -- -D warnings: passed.
• cargo fmt --all -- --check, git diff --check, and canonical module-size gate: passed.
• Real pre-push router passed version sync, skills validation, module-size, and all-target/all-feature Clippy.
• Remote head: a5d0de6130527ae466dc25e9f645d88c20c01391.
• Base includes merged W16 artifact-evidence foundation from PR feat: add W16 artifact evidence foundation #198.

Detailed implementation evidence is tracked in docs/plans/agent-observatory/proof/PROOF.md.

Next slices

This PR remains draft while the same lane continues through AO-047+ histogram/exponential/summary normalization, metric persistence, /v1/metrics, and subsequent API hardening.