memory: confidence axis + contradiction supersession

[yogthos]

Phase 2 of applying the Elastic agent-memory ideas. This is idea #4 (confidence), bundled with supersession per the lesson from migration v9/dirge-lerb: a bare confidence column was reverted once for being write-only, so this time it ships with both a producer that varies it and consumers that read it.

What changed

• Schema v13: re-adds confidence REAL (default 0.6) and superseded_at; superseded_by (inert since v7) now holds the successor uid.
• Confidence is genuinely read — the whole point:
  • Eviction: folded into effective salience as a tiebreak among equal-salience entries (bounded ±0.1 so it never jumps the kind hierarchy).
  • Search: confidence DESC tiebreak after relevance/salience.
  • Curation: annotated in the curator render ([kind | N uses | conf C | id]) so the LLM curator can verify/re-confidence contested facts.
  • View: surfaced in lifecycle meta.
• Supersession (the producer): new supersede action retires a contradicted fact to status='superseded' — excluded from snapshot/views/search/eviction exactly like a tombstone, but kept as an audit record (superseded_by/superseded_at) — and writes the corrected fact as a new entry. harsh=true (user flatly denied the old fact) discounts the successor to 0.5; a natural update lands at 0.7.
• Producer wiring: the background review pass gets a "supersede contradicted facts" instruction. supersede is in the tool enum but kept out of SYSTEM_PROMPT, consistent with the Phase 1 treatment of background-driven actions.
• Refactor: add_entry's hot-tier compaction extracted to a shared insert_into_hot so supersede reuses the working-reserve rules rather than duplicating them.

Review notes

A /code-review high pass (3 finder angles) ran on the diff. Acted on:

• Made the "read in curation" claim true — the curator render now surfaces confidence (it was claimed but not wired); this is the dirge-lerb trap and was the top finding.
• Added a production-value eviction test (a harsh-superseded fact at 0.5 evicts before a default 0.6 sibling via the real path, not forced UPDATEs) and made the eviction-weight doc honest about its tiebreak role.
• Fixed two stale comments (orphaned compaction comment; the "confidence column is gone" import comment) and documented supersession as terminal (recovery is to re-add, not restore — reviving alongside the successor would create competing facts).

Migration interaction: v9 dropped confidence and v13 re-adds it, so a pre-v9 DB round-trips to a fresh default; the v9 test now covers the drop-then-re-add.

Tests

New tests: supersession retire/audit-chain, harsh confidence discount, snapshot exclusion + persistence, eviction-by-confidence (forced and production values), default confidence + view surfacing, curator annotation, and the v13 migration. Full suite green (2790), clippy + fmt clean.

bd: dirge-fa10