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>

tsconfig.json

@@ -13,10 +13,9 @@
     "resolveJsonModule": true,
     "isolatedModules": true,
     "types": ["node"],
-    "baseUrl": ".",
     "paths": {
-      "@shared/*": ["src/shared/*"],
-      "@main/*": ["src/main/*"]
+      "@shared/*": ["./src/shared/*"],
+      "@main/*": ["./src/main/*"]
     }
   },
   "include": ["src/**/*", "tests/**/*"],