docs: reframe observations as evidence-grounded consolidated knowledge

[nicoloboschi]

Summary

The docs currently describe observations as "auto-synthesized patterns" / "synthesized knowledge representations". That framing reads as LLM summarization and undersells what observations actually are per the code (hindsight-api-slim/hindsight_api/engine/consolidation/consolidator.py, engine/reflect/observations.py):

• Deduplicated, not re-summarized — overlapping facts merge into one durable belief with a proof_count, not repeated observations.
• Evidence-grounded — each observation references its source memories with exact quotes (ObservationEvidence.quote).
• Refined, not overwritten — contradictions are incorporated while preserving history.
• Freshness trend computed from evidence timestamps (stable / strengthening / weakening / new / stale).

This PR updates the five spots that used the old framing to describe what observations really are.

Files changed

• hindsight-docs/src/pages/best-practices.mdx — taxonomy row + memory-type row
• hindsight-docs/docs/developer/api/recall.mdx — types parameter description + observation tip
• hindsight-docs/docs/developer/observations.mdx — page intro, "What Are Observations?", bullet list
• hindsight-docs/docs/developer/index.mdx — consolidation overview
• hindsight-docs/docs/developer/configuration.md — observations section intro + `OBSERVATIONS_MISSION` description

Docs-only, no code or schema changes.

Test plan

• Build docs site locally (`./scripts/dev/start-docs.sh`) and spot-check the five edited pages render cleanly
• Verify no broken internal links introduced