Collapse WhatsApp Web to a Signal-style avatar rail in slim windows (#6473)

* Make menu overflow visible with a half-row peek and edge fades

Menus used to cut off clean at ten rows, so anything below the fold was
undiscoverable. Now the list sizes to what fits within 60% of the screen
and always ends mid-row when items overflow, with scroll-position-driven
fades at both edges. Keyboard navigation keeps the next hidden row peeking
past the cursor so the fold affordance travels with the selection.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* Collapse WhatsApp Web to a Signal-style avatar rail in slim windows

Add a WhatsApp Slim Chromium extension that injects CSS into
web.whatsapp.com, collapsing the chat list to a 90px avatar rail with
floating unread badges when the window is narrower than 1100px. Wide
windows keep the stock layout.

Loaded through the existing --load-extension list in chromium-flags.conf,
with a migration to append it for existing users.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

default/chromium/extensions/whatsapp-slim/manifest.json

@@ -0,0 +1,12 @@
+{
+  "manifest_version": 3,
+  "name": "WhatsApp Slim",
+  "version": "1.0",
+  "description": "Collapse WhatsApp Web's chat list to an avatar rail in narrow windows, this extension is installed by Omarchy",
+  "content_scripts": [
+    {
+      "matches": ["https://web.whatsapp.com/*"],
+      "css": ["whatsapp.css"]
+    }
+  ]
+}