feat(main): add Electron entry + Inbox window shell

Task 2 of the slice plan. Creates the minimal Electron main
process: app entry that opens an Inbox BrowserWindow on
whenReady, an inboxWindow module that handles show/hide/close-
to-tray semantics, an HTML placeholder renderer ("Inkling Inbox
(renderer pending)"), and the minimum @shared/types augmentation
for app.isQuitting (Task 3 expands this file).

Plan tsconfig template adjustment: TypeScript 6 deprecates
baseUrl. Dropped it and made paths entries explicitly relative
("./src/...") so they resolve from tsconfig.json's directory.
Updated both the in-repo tsconfig.json and Task 1 Step 3 in the
plan to match.

Verification: `npm run typecheck` exits 0. Full `npm run dev`
sanity check is deferred until Task 3 (preload) and Task 19
(quickcapture HTML) land — electron-vite.config.ts wires both
entries that don't yet exist.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/main/windows/inboxWindow.ts

@@ -0,0 +1,46 @@
+import { BrowserWindow, app } from 'electron';
+import { join } from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+let inboxWindow: BrowserWindow | null = null;
+const __dirname = fileURLToPath(new URL('.', import.meta.url));
+
+export function getInboxWindow(): BrowserWindow | null {
+  return inboxWindow;
+}
+
+export function createInboxWindow(): BrowserWindow {
+  if (inboxWindow && !inboxWindow.isDestroyed()) {
+    inboxWindow.show();
+    inboxWindow.focus();
+    return inboxWindow;
+  }
+
+  inboxWindow = new BrowserWindow({
+    width: 900,
+    height: 720,
+    show: false,
+    webPreferences: {
+      preload: join(__dirname, '../preload/index.js'),
+      contextIsolation: true,
+      nodeIntegration: false,
+      sandbox: false
+    }
+  });
+
+  if (process.env.ELECTRON_RENDERER_URL) {
+    inboxWindow.loadURL(`${process.env.ELECTRON_RENDERER_URL}/inbox/index.html`);
+  } else {
+    inboxWindow.loadFile(join(__dirname, '../renderer/inbox/index.html'));
+  }
+
+  inboxWindow.on('close', (e) => {
+    if (!app.isQuitting) {
+      e.preventDefault();
+      inboxWindow?.hide();
+    }
+  });
+
+  inboxWindow.once('ready-to-show', () => inboxWindow?.show());
+  return inboxWindow;
+}