fix(machine): re-pair wipes the prior operator's config + watermarks (#70)

A new-seed re-pair UPSERTed the bunker binding but left fee_config, cassettes,
and the created_at replay watermarks intact. The watermarks are the trap: a new
backend whose first config event has a lower created_at than the old operator's
last event is silently dropped as a replay, so re-pairing a long-lived install
to a fresh backend appears to pair but never picks up new config.

Add resetForRepair() (main-process state-store): in one transaction it clears
fee_config and resets both replay watermarks to 0. Wired function → IPC
(state:reset-for-repair) → preload → renderer, and called from the re-pair branch
in signer-resolver, gated on an existing binding (re-pair only; a first pair has
nothing to reset). Deliberately preserves cassettes/cashbox/transactions — those
track PHYSICAL cash that survives an operator handover; a full wipe is the
factory-reset path.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/machine/electron/main.ts

@@ -27,6 +27,7 @@ import {
   getBootstrapPublishedAt,
   markBootstrapPublished,
   resetBootstrapGate,
+  resetForRepair,
   applyOperatorCassettesConfig,
   getFeeConfig,
   getLastKnownFeeConfigCreatedAt,
@@ -355,6 +356,9 @@ ipcMain.handle('state:clear-bunker-binding', (): void => {
 ipcMain.handle('state:reset-bootstrap-gate', (): void => {
   resetBootstrapGate()
 })
+ipcMain.handle('state:reset-for-repair', (): void => {
+  resetForRepair()
+})
 
 // QR-pairing wizard (aiolabs/bitspire#52): an unpaired machine scans a
 // spire-seed off its camera, and we persist it as VITE_SPIRE_SEED in the