feat(proxy/store): add the learn v3 sink detectors

Five new detectors plus a widened cache-hygiene pass, all ranked and priced
through the same path as the existing sinks rather than appended afterwards:

- cache_efficiency (detect_cache_hygiene.go): what a million input tokens
  actually cost after this user's cache reuse, and the multiplier against list.
  It is the rate the other sinks are priced at, so it carries no token volume
  and must never be summed with them. Per-turn hooks are listed as candidates,
  caveman's own included.
- tool_output_portfolio: the call shapes that dominate context, ranked by
  normalized signature. No paths or arguments survive normalization.
- session_outcomes: token share in sessions with no commit in their window.
  Fails closed — a repo git cannot answer is dropped, never counted as
  commitless. Correlational, and framed that way.
- subagent_spend: sidechain token share and per-type spawn counts. Visibility
  only; it carries no practice id and never becomes "spawn fewer subagents".
- procedure_repeat:*: distillation candidates mined from tool-signature
  n-grams, routed away from the net-token-negative gate because a skill's cost
  and its benefit land in different places.
- config_growth (detect_config_trend.go): growth against this machine's own
  snapshot history, not against a guideline. Reports the delta only so it never
  double-counts the config weight sink.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>