v1.108.53 — recency window on weight tuning

tune_weights now learns from a recency window of the ranking ledger (new max_age_days parameter, default 90 days) instead of the lifetime history. Previously, every ranking event ever recorded for a repo fed the semantic_weight / identity_boost proposals, so as a codebase and its query patterns evolved, stale events kept anchoring the learned weights to a distribution that no longer exists. Recent research on memory systems documents exactly this failure mode: accumulated context that cannot distinguish current from stale signal degrades retrieval quality over time.

Set max_age_days=0 to restore the lifetime read. Per-repo results and the tool summary now report the window used.

Full notes in CHANGELOG.md.