Adds circuitforge_core.preferences.currency with get/set_currency_code()
and format_currency(). Priority chain: store → CURRENCY_DEFAULT env → USD.
Formatting uses babel when available; falls back to a 30-currency symbol
table with correct ISO 4217 minor-unit decimal places (0 for JPY, KRW, etc.).
Consumed by Snipe, Kiwi, Peregrine, Crossbill. Bumps to v0.13.0.
12 signal functions covering staleness, repost patterns, salary transparency,
ATS blackhole detection, and enrichment signals. All pure functions — no LLM,
no network, no I/O. trust_score = 1 - sum(triggered weights), clamped to [0,1].
confidence reflects fraction of signals with available evidence.
Salary transparency enforced for CO/CA/NY/WA/IL/MA. ATS blackhole patterns:
Lever, Greenhouse, Workday, iCIMS, Taleo.
83 tests (models, all 12 signals individually, scorer). Bumps to v0.12.0.
