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>

migrations/1785543725.sh

@@ -0,0 +1,20 @@
+echo "Add WhatsApp Slim extension to Chromium-based browsers"
+
+WHATSAPP_SLIM_EXT="$OMARCHY_PATH/default/chromium/extensions/whatsapp-slim"
+
+add_whatsapp_slim_extension() {
+  local file=$1
+
+  [[ -f $file ]] || return 0
+  grep -q "extensions/whatsapp-slim" "$file" && return 0
+
+  if grep -q "^--load-extension=" "$file"; then
+    sed -i --follow-symlinks "s|^--load-extension=\(.*\)$|--load-extension=\1,$WHATSAPP_SLIM_EXT|" "$file"
+  else
+    echo "--load-extension=$WHATSAPP_SLIM_EXT" >>"$file"
+  fi
+}
+
+for conf in chromium chrome google-chrome brave brave-beta brave-nightly brave-origin-beta microsoft-edge-stable; do
+  add_whatsapp_slim_extension "$HOME/.config/$conf-flags.conf"
+done