calibration: generalize backtest-gated loosening into a bounded knob registry beyond the satisfaction floor

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Problem

The #8121 narrow start hardcodes ONE loosenable knob (the satisfaction floor). The epic's full intent is a registry of loosenable configuration values, each with its own hard safety bounds, all gated on the same backtest discipline.

Requirements

⚠️ Required pattern. Mirror KNOWN_THRESHOLDS (src/services/threshold-backtest.ts) / KNOWN_LOGIC_RULES (scripts/backtest-logic-check-core.ts): a declarative registry mapping each knob to its rule ids, candidate steps, and hard bounds — never per-knob bespoke loops.

• Every knob keeps the narrow start's invariants: smallest-step-first, visible-improved + held-out-non-regressed, hard minimum, write-path direction re-checks, audit event per apply.
• Do not add a knob without real fired/override ground truth for its rule ids.

Deliverables

• The registry + generalized evaluator (refactor of satisfaction-floor-loosening.ts, keeping its tests green)
• At least one additional knob wired end-to-end with its own bounds and tests

Links & Resources

#8121 (parent), src/services/satisfaction-floor-loosening.ts (the shape to generalize)
maintainer-only — extends autonomous config change; each knob is a deliberate decision.

[linear-code]

JSO-5660