Add structured ingest traceability

[ethanj]

Summary

Adds structured ingest traceability to atomicmemory-core so benchmark and debugging workflows can inspect why each fact was stored, skipped, updated, or deleted.

This change:

• adds a config-gated ingest trace collector that persists structured JSON trace artifacts
• surfaces ingest_trace_id on ingest responses when tracing is enabled
• records per-fact decision metadata across direct store, quick dedup, fast AUDN, deferred AUDN, LLM AUDN, write-security, entropy-gate, and verbatim ingest paths
• makes ingest trace output configurable with INGEST_TRACE_DIR
• hardens the ingest trace contract with closed action and reason-code unions
• regenerates OpenAPI so the response shape stays in sync

Testing

• dotenv -e .env.test -- pnpm exec tsc --noEmit
• dotenv -e .env.test -- pnpm test src/services/__tests__/ingest-trace-branches.test.ts src/services/__tests__/ingest-trace.test.ts src/__tests__/memory-route-config-override.test.ts src/services/__tests__/retrieval-trace.test.ts src/__tests__/config-partition.test.ts src/__tests__/route-validation.test.ts --reporter verbose
• dotenv -e .env.test -- npm test
• dotenv -e .env -- pnpm build
• fallow (still reports pre-existing repo-wide duplication/complexity debt outside this PR; no auto-fixes available)

Notes

• OpenAPI artifacts were regenerated as part of this change.
• The pre-existing performStoreVerbatim write-security behavior is intentionally not changed here; this PR is scoped to observability and trace-contract hardening.