Retire the request-time hint API. PR-B5 splits TOIN into two phases:
1. Observation: TOIN keeps recording compressions/retrievals at runtime,
but `get_recommendation()` is deprecated and now returns None.
2. Publish-then-load: the new `headroom.cli.toin_publish` CLI walks the
on-disk store and emits `recommendations.toml`. The Rust proxy reads
that file once at startup via `transforms::recommendations` and
exposes `get(auth_mode, model, structure_hash) -> Option<&Rec>`.
PR-F3 will wire the loader into the live-zone dispatcher.
Per-tenant aggregation: `_patterns` is now keyed by
`(auth_mode, model_family, sig_hash)` so PAYG/OAuth/subscription tenants
no longer share buckets. Callers that don't supply auth/model land in the
`("unknown", "unknown", sig_hash)` slot. Added `_make_pattern_key` helper
+ updated tests that previously indexed by raw `structure_hash`.
AuthMode is canonical in `transforms::live_zone`; `transforms::recommendations`
re-exports it (no duplicate enum). Live-zone enum gained `Unknown`,
`as_str()`, and `Hash` derive to serve recommendations callers without a
second source of truth.
Why: per-request hint calls coupled output to mutable TOIN state, breaking
prompt-cache stability across runs (P2-27, P5-56). Pulling advice into a
startup-published TOML keeps per-request output deterministic and lets the
deploy pipeline gate publication independently of proxy uptime.
Per-PR-B5 plan: REALIGNMENT/04-phase-B-live-zone.md.
