feat(machine): add SQLite persistence and remove npub linking

Add crash-safe persistence for cassette inventory, cashbox state, and
transaction history using better-sqlite3 in the Electron main process.
The state machine now loads inventory from the database at runtime
instead of using hardcoded values, and transactions are automatically
persisted on completion.

Remove the unnecessary npub linking code — Lightning.Pub auto-creates
and associates Nostr users when appId is included in RPC requests,
making the HTTP-based user creation and token linking redundant.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/machine/electron/preload.ts

@@ -19,7 +19,6 @@ export interface RuntimeConfig {
   atmPrivateKey: string
   adminToken: string
   appId: string
-  appToken: string
   machineModel: string
   fiatCode: string
   validatorDevice?: string
@@ -35,6 +34,21 @@ contextBridge.exposeInMainWorld('electronAPI', {
   // Get runtime configuration (read from environment at runtime)
   getConfig: (): Promise<RuntimeConfig> => ipcRenderer.invoke('get-config'),
 
+  // State persistence
+  loadCassettes: () => ipcRenderer.invoke('state:load-cassettes'),
+  setCassettes: (cassettes: { denomination: number; count: number }[]) =>
+    ipcRenderer.invoke('state:set-cassettes', cassettes),
+  getInventory: () => ipcRenderer.invoke('state:get-inventory'),
+  getCashbox: () => ipcRenderer.invoke('state:get-cashbox'),
+  recordTransaction: (tx: {
+    txid: string
+    type: 'cash_in' | 'cash_out'
+    fiatCents: number
+    sats: number
+    bills: { denomination: number; count: number }[]
+  }) => ipcRenderer.invoke('state:record-transaction', tx),
+  emptyCashbox: () => ipcRenderer.invoke('state:empty-cashbox'),
+
   // Platform info
   platform: process.platform,
 })
@@ -45,6 +59,22 @@ declare global {
     electronAPI: {
       getVersion: () => Promise<string>
       getConfig: () => Promise<RuntimeConfig>
+      loadCassettes: () => Promise<{ denomination: number; count: number }[]>
+      setCassettes: (cassettes: { denomination: number; count: number }[]) => Promise<void>
+      getInventory: () => Promise<Record<number, number>>
+      getCashbox: () => Promise<{
+        totalBills: number
+        totalFiatCents: number
+        lastEmptiedAt: number | null
+      }>
+      recordTransaction: (tx: {
+        txid: string
+        type: 'cash_in' | 'cash_out'
+        fiatCents: number
+        sats: number
+        bills: { denomination: number; count: number }[]
+      }) => Promise<void>
+      emptyCashbox: () => Promise<void>
       platform: NodeJS.Platform
     }
   }