chore(vnc): bootstrap VNCmail+ fork — vnc/ layer + Vercel runbook

Fork of bulwarkmail/webmail for deploy on Vercel as project vncmail-plus.
Adds vnc/ customization layer (branding, overrides, VNC-CHANGES log),
Vercel env template, and VNCMAIL-SETUP.md runbook. No upstream files touched.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

vnc/branding/README.md

@@ -0,0 +1,19 @@
+# vnc/branding
+
+Drop VNCmail+ brand assets here (logos, favicon, PWA icons), then point the
+runtime branding env vars at them. Most branding needs **no code edit** — it's
+all env-driven and read at runtime.
+
+Suggested assets:
+- `logo-light.svg` / `logo-dark.svg`  → `APP_LOGO_LIGHT_URL` / `APP_LOGO_DARK_URL`
+- `login-logo-light.svg` / `login-logo-dark.svg` → `LOGIN_LOGO_LIGHT_URL` / `LOGIN_LOGO_DARK_URL`
+- `favicon.ico` → `FAVICON_URL`
+- `pwa-icon.png` (512×512) → `PWA_ICON_URL`
+
+To serve these from the app itself, copy them into `public/branding/` and set the
+URLs to `/branding/<file>`. To serve from a CDN, set absolute URLs.
+
+Theme colors: `PWA_THEME_COLOR`, `PWA_BACKGROUND_COLOR`.
+
+See `VNCMAIL-SETUP.md` and upstream `.env.example` (branding section) for the full
+list.