Ε-F1 proprietary RSBK; Ε-F2 always a new bank with an auto suffix; Ε-F3 refuse import on a degraded ledger.
Adds docs/product/bank-package.md and the Phase Ε spec in docs/PLAN.md: three waves, six tracks. Three forks open; Ε-F1 blocks Ε-W1-T1.