fix(notifications): Advanced Push Rules mode switch keeps highlight/sound tweaks

RuleModeSwitcher rebuilt a rule's actions from scratch, so changing the
mode of e.g. .m.rule.is_user_mention silently dropped its highlight tweak
account-wide. Derive the existing highlight/custom-sound tweaks from the
rule's current actions and pass them through as NotificationModeOptions.
Adds getNotificationModeOptionsFromActions + unit tests.

Fixes #19

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/hooks/useNotificationMode.ts

@@ -49,6 +49,29 @@ export const getNotificationModeActions = (
   return actions;
 };
 
+// Derive the options that would reproduce an existing rule's tweaks, so a mode
+// switch rebuilds actions on top of them instead of silently dropping a
+// `highlight` tweak (or a custom sound) that isn't part of the mode itself.
+export const getNotificationModeOptionsFromActions = (
+  actions: PushRuleAction[],
+): NotificationModeOptions => {
+  const soundTweak = actions.find(
+    (action) => typeof action === 'object' && action.set_tweak === TweakName.Sound,
+  );
+  const highlightTweak = actions.find(
+    (action) => typeof action === 'object' && action.set_tweak === TweakName.Highlight,
+  );
+
+  return {
+    soundValue:
+      soundTweak && typeof soundTweak === 'object' && typeof soundTweak.value === 'string'
+        ? soundTweak.value
+        : undefined,
+    highlight:
+      !!highlightTweak && typeof highlightTweak === 'object' && highlightTweak.value !== false,
+  };
+};
+
 export type GetNotificationModeCallback = (mode: NotificationMode) => PushRuleAction[];
 export const useNotificationModeActions = (
   options?: NotificationModeOptions,