Harden browser policy directories (#7972)

Cherry-picked from quattro (7d58bb9a).

Stop world-writable Chromium and Firefox policy directories: create them
root-owned at 0755, purge non-root entries, refuse planted symlinks, and
write the browser theme colour through a passwordless helper instead of
a world-writable policy file.

Conflict resolution for v4-0-2:
- bin/omarchy-install-browser: dropped the `chromium)` case, which does
  not exist on this branch.
- test/shell.d/default-apps-test.sh: dropped; the file does not exist on
  this branch.

bin/omarchy-install-browser

@@ -4,9 +4,10 @@
 # omarchy:args=<chrome|brave|brave-origin|edge|firefox|zen>
 # omarchy:examples=omarchy install browser firefox | omarchy install browser brave
 
-setup_policy_directory() {
-  sudo mkdir -p "$1"
-  sudo chmod a+rw "$1"
+source "$OMARCHY_PATH/install/helpers/browser-policy.sh"
+
+setup_chromium_policy_directory() {
+  browser_policy_setup_dir "$1"
 }
 
 announce_browser_installed() {
@@ -21,13 +22,6 @@ copy_chromium_flags() {
   omarchy-install-chromium-ytdlp
 }
 
-setup_firefox_preferences() {
-  local distribution_dir="$1"
-
-  setup_policy_directory "$distribution_dir"
-  sudo cp -f "$OMARCHY_PATH/default/firefox/policies.json" "$distribution_dir/policies.json"
-}
-
 setup_firefox_wayland() {
   mkdir -p ~/.config/environment.d
   echo "MOZ_ENABLE_WAYLAND=1" > ~/.config/environment.d/omarchy-firefox-wayland.conf
@@ -38,7 +32,7 @@ chrome)
   echo "Installing Chrome..."
   omarchy-pkg-aur-add google-chrome || exit 1
 
-  setup_policy_directory /etc/opt/chrome/policies/managed
+  setup_chromium_policy_directory /etc/opt/chrome/policies/managed
   copy_chromium_flags ~/.config/chrome-flags.conf
   omarchy-theme-set-browser
   announce_browser_installed "Chrome"
@@ -47,7 +41,7 @@ edge)
   echo "Installing Edge..."
   omarchy-pkg-aur-add microsoft-edge-stable-bin || exit 1
 
-  setup_policy_directory /etc/opt/edge/policies/managed
+  setup_chromium_policy_directory /etc/opt/edge/policies/managed
   copy_chromium_flags ~/.config/microsoft-edge-stable-flags.conf
   omarchy-theme-set-browser
   announce_browser_installed "Edge"
@@ -56,7 +50,7 @@ brave)
   echo "Installing Brave..."
   omarchy-pkg-aur-add brave-bin || exit 1
 
-  setup_policy_directory /etc/brave/policies/managed
+  setup_chromium_policy_directory /etc/brave/policies/managed
   copy_chromium_flags ~/.config/brave-flags.conf
   omarchy-theme-set-browser
   announce_browser_installed "Brave"
@@ -65,7 +59,7 @@ brave-origin)
   echo "Installing Brave Origin..."
   omarchy-pkg-aur-add brave-origin-bin || exit 1
 
-  setup_policy_directory /etc/brave/policies/managed
+  setup_chromium_policy_directory /etc/brave/policies/managed
   copy_chromium_flags ~/.config/brave-origin-flags.conf
   omarchy-theme-set-browser
   announce_browser_installed "Brave Origin"
@@ -74,7 +68,7 @@ firefox)
   echo "Installing Firefox..."
   omarchy-pkg-add firefox || exit 1
 
-  setup_firefox_preferences /usr/lib/firefox/distribution
+  browser_policy_setup_firefox_distribution /usr/lib/firefox/distribution
   setup_firefox_wayland
   announce_browser_installed "Firefox"
   ;;
@@ -82,7 +76,7 @@ zen)
   echo "Installing Zen..."
   omarchy-pkg-aur-add zen-browser-bin || exit 1
 
-  setup_firefox_preferences /opt/zen-browser/distribution
+  browser_policy_setup_firefox_distribution /opt/zen-browser/distribution
   setup_firefox_wayland
   announce_browser_installed "Zen"
   ;;