fix: backport Hindsight consolidation race handling - #32

Summary

• backport vectorize-io/hindsight PR #2620 to the pinned Hindsight 0.8.4 image
• skip best-effort observation history writes when parallel consolidation has already removed the source observation
• publish the patched local image as telefire-hindsight:0.8.4-hardened-r1

Why

The live Telegram command matrix passed, but its revision-heavy memory flow exposed Hindsight's known observation_history_observation_id_fkey consolidation race. A queued consolidation recovered afterward, but the failed background operation made the deployment audit noisy and could delay future consolidation work.

Verification

• uv run pytest -q (267 passed, 6 skipped)
• rebuilt telefire-hindsight:0.8.4-hardened-r1
• exercised _append_observation_history in the built image with a synthetic asyncpg.exceptions.ForeignKeyViolationError
• confirmed the patched image still omits the package managers removed by the hardened base
• docker compose ... config --images
• git diff --cached --check

Upstream: vectorize-io/hindsight#2620