feat(machine): add markdown-driven support pages

Add support/help pages accessible via a ? button on the idle screen.
Pages are driven by .md files in /var/lib/lamassu-atm/support/ —
operators can customize content without rebuilding the app.

Features:
- Tabbed view with markdown rendering (via marked)
- Standalone URLs auto-render as QR codes (scannable from phone)
- Table URLs: click-to-reveal QR codes (prevents accidental scans)
- Yes/No rendered as green checkmarks / red X marks
- Wallet comparison table with download QR codes
- FAQ with Lightning-only clarification
- Support page with operator Nostr QR placeholder
- Custodial vs non-custodial footnote
- Large text for touchscreen accessibility
- Centered layout for short-content pages

Closes #36

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/machine/electron/main.ts

@@ -227,6 +227,29 @@ ipcMain.handle('state:remediate-transaction', (_event, txid: string, remediatedB
   remediateTransaction(txid, remediatedByTxid)
 )
 
+// Support pages — read .md files from /var/lib/lamassu-atm/support/
+ipcMain.handle('support:get-pages', () => {
+  const supportDir = path.join(
+    fs.existsSync('/var/lib/lamassu-atm') ? '/var/lib/lamassu-atm' : process.cwd(),
+    'support'
+  )
+  if (!fs.existsSync(supportDir)) return []
+
+  const files = fs
+    .readdirSync(supportDir)
+    .filter((f) => f.endsWith('.md'))
+    .sort()
+  return files.map((file) => {
+    const content = fs.readFileSync(path.join(supportDir, file), 'utf-8')
+    const titleMatch = content.match(/^#\s+(.+)/m)
+    return {
+      id: file.replace('.md', ''),
+      title: titleMatch ? titleMatch[1] : file.replace('.md', ''),
+      content,
+    }
+  })
+})
+
 // =============================================================================
 // HAL Hardware IPC Handlers
 // HAL runs in the main process (Node.js) because it needs serialport.