fix biometric, tx dedup, loading crash; add flush cache; remove monero startup from evm init

- biometric-helper: use .deviceOwnerAuthentication so passcode can
  unlock Touch ID when biometrics are locked out
- get-transaction-history: dedup transfers by hash+category+contract
  instead of hash alone (was dropping token transfers sharing a tx hash)
- evm-wallet.svelte.ts: add missing loading  declaration (caused
  ReferenceError on createWallet); add flushTxCache method; comment out
  monero startup from evm init to speed up loading
- get-history.ts: remove dead caching logic (now handled by sync engine);
  import getTransactionHistory from alchemy directly
- backend RPC + settings UI: add flushTxCache to clear tx cache tables

apps/desktop/src/routes/settings.svelte

@@ -17,6 +17,7 @@
 	let confirm = $state(false)
 	let resetting = $state(false)
 	let deletingWalletId = $state<string | null>(null)
+	let flushing = $state(false)
 
 	async function handleReset() {
 		resetting = true
@@ -31,6 +32,12 @@
 		deletingWalletId = null
 		if (w.wallets.length === 0) navigate('/multicoin')
 	}
+
+	async function handleFlushCache() {
+		flushing = true
+		await w.flushTxCache()
+		flushing = false
+	}
 </script>
 
 <div class="mx-auto mt-16 max-w-md">
@@ -84,6 +91,17 @@
 				<CardDescription>App preferences and data management</CardDescription>
 			</CardHeader>
 			<CardContent class="space-y-4">
+				<div>
+					<p class="font-medium text-xs">Transaction Cache</p>
+					<p class="text-muted-foreground text-xs mt-1">
+						Clears all cached transaction history and sync status. Data will be re-fetched from Alchemy on next refresh.
+					</p>
+					<div class="mt-3">
+						<Button variant="outline" onclick={handleFlushCache} disabled={flushing}>
+							{flushing ? 'Flushing...' : 'Flush Transaction Cache'}
+						</Button>
+					</div>
+				</div>
 				<div>
 					<p class="font-medium text-xs">Reset App</p>
 					<p class="text-muted-foreground text-xs mt-1">