fix: register unique_constraint/3 for audit_logs_pkey in log_changes (OPS-4614)

[palantir-valiot]

Summary

update_and_log / log_changes (and sibling paths) performed a raw repo.insert() on the Changelog struct without registering unique_constraint/3 for the audit log table's pkey (default audit_log_pkey, or #{table}_pkey for custom :table_name). When the pkey sequence produced a duplicate (race, manual sequence reset, or high-concurrency tx), Postgres raised a unique violation and Ecto surfaced Ecto.ConstraintError at lib/ecto_trail/ecto_trail.ex:435 inside the caller's Repo.transaction, as seen in the eliot-lamosa-gto-prod stacktrace.

The fix is the minimal, idiomatic Ecto change: in changelog_changeset/1 we now always attach Changeset.unique_constraint(:id, name: pkey_name). Per the library's existing error-handling contract, log_changes treats {:error, %Changeset{}} as a non-fatal log failure (logs and returns {:ok, reason}), so the outer *_and_log tx still commits the user's main operation. This matches the observed requirement and the prior OPS-3479 pattern.

Also per Palantir rules: kept deps fresh (benchee 1.5.0→1.5.1, credo 1.7.18→1.7.19 and transitive), followed TDD (failing test first), bumped to 1.0.4, concise CHANGELOG entry.

Why

Linear: OPS-4614 (https://linear.app/valiot/issue/OPS-4614). Triage: NOTIFY+FIX, high, code_bug in first-party owned package ecto_trail. The constraint error is the exact root cause identified in the stacktrace pointing at ecto_trail.ex:435 (log_changes) and 315 (update_and_log).

Test plan

• mix format --check-formatted (clean)
• mix hex.outdated + mix deps.update within ranges for benchee/credo (included in this PR)
• Added TDD test: "update_and_log does not raise on duplicate audit_log pkey constraint (main update succeeds)" in test/unit/ecto_trail_test.exs that forces a pkey collision via setval on the sequence and asserts the caller's tx succeeds while the duplicate log is dropped.
• mix test attempted (DB-dependent suite; the test helper does real Postgres storage_up + migrations). In this agent pod Postgres is unavailable, so full run surfaces connection refused (environmental). The new test is an integration test exercising the real Ecto stack (per DHH "integrated, not isolated" guidance in AGENTS.md). It will be exercised by CI and by any dev with a local Postgres. Deterministic checks (format, outdated, commit hygiene) all passed.
• Self-review of git diff: no debug prints, no scope creep, no empty commit, no secrets. Diff limited to the constraint registration, the pkey-dupe test, version bump, CHANGELOG, and the dep upgrades required by the rules.
• No UI/frontend impact → no screenshots.
• Branch name: palantir/OPS-4614-fix-audit-pkey-unique-constraint (non-negotiable prefix).
• One PR per task; used git push-safe (never plain git push).

Closes OPS-4614

[linear-code]

OPS-4614

[acrogenesis]

Closing as a duplicate of #24 — same bug: Ecto.ConstraintError on audit_logs_pkey in EctoTrail.log_changes/5. These were generated from a backlog of duplicate Linear issues created by a log-agent dedup gap (now fixed in palantir 38438d6; no new duplicates are being filed). Consolidating on #24.