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/overrides/README.md

@@ -0,0 +1,15 @@
+# vnc/overrides
+
+Home for VNC-specific UI overrides that go beyond env-driven branding.
+
+Keep changes here (and imported into upstream files with a **single, logged**
+edit) rather than editing upstream components in place — it keeps
+`git merge upstream/main` cheap.
+
+Pattern:
+- Put a replacement component / theme token / CSS layer in this folder.
+- Wire it in with the smallest possible edit to the upstream file.
+- Record that edit in `../VNC-CHANGES.md`.
+
+If you find yourself editing many upstream files for one feature, stop and
+reconsider whether it can be an override or an upstream contribution instead.