Add localhost screenshot endpoint and email-upload guide

- Electron main now exposes http://127.0.0.1:9990/screenshot that returns
  a PNG via CDP Page.captureScreenshot (GNOME Wayland blocks external
  capture, and webContents.capturePage() hangs on this compositor). The
  endpoint is localhost-only.
- EMAIL_UPLOAD.md documents the n8n IMAP -> Samba share workflow for
  Skylight-style email-to-photo-frame uploads.

electron/main.ts

@@ -1,6 +1,7 @@
 import { app, BrowserWindow, ipcMain, screen, powerSaveBlocker } from 'electron';
 import * as path from 'path';
 import * as fs from 'fs';
+import * as http from 'http';
 import { ScreenManager } from './services/ScreenManager';
 import { PresenceDetector } from './services/PresenceDetector';
 import { FrigateStreamer } from './services/FrigateStreamer';
@@ -230,6 +231,34 @@ app.on('window-all-closed', () => {
   }
 });
 
+// Localhost-only HTTP endpoint for self-screenshots. GNOME Wayland blocks
+// external screen capture, but webContents.capturePage() works from inside.
+// Usage: curl -s http://127.0.0.1:9990/screenshot > out.png
+http
+  .createServer(async (req, res) => {
+    if (req.url === '/screenshot' && mainWindow) {
+      try {
+        const wc = mainWindow.webContents;
+        if (!wc.debugger.isAttached()) wc.debugger.attach('1.3');
+        const result = (await wc.debugger.sendCommand('Page.captureScreenshot', {
+          format: 'png',
+          captureBeyondViewport: false,
+        })) as { data: string };
+        res.setHeader('Content-Type', 'image/png');
+        res.end(Buffer.from(result.data, 'base64'));
+      } catch (err) {
+        res.statusCode = 500;
+        res.end(String(err));
+      }
+    } else {
+      res.statusCode = 404;
+      res.end();
+    }
+  })
+  .listen(9990, '127.0.0.1', () => {
+    console.log('Screenshot endpoint on http://127.0.0.1:9990/screenshot');
+  });
+
 // Handle uncaught exceptions
 process.on('uncaughtException', (error) => {
   console.error('Uncaught exception:', error);