fix(health): Fix button must not act when the switch was cancelled

Vault health → Fix on entry B while the editor is open and dirty on entry A:
the discard prompt appears, Cancel keeps A open — but openEntryForFix carried
on regardless. It unmasked A's password to cleartext, selected it, and pulsed
the Generate button (the blinking). Wrong entry, and it revealed a password
the user never asked to see.

openSlideOver was void, so callers couldn't tell a cancelled switch from a
successful one. It now returns false when it bails (discard cancelled, entry
not found) and true once the panel actually shows the requested entry;
openEntryForFix checks it before touching the password field.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

js/app.health.js

@@ -93,7 +93,10 @@ function healthScoreBand(score) {
 // dismiss. Auto-opening the generator modal hid the entry context and
 // forced an extra Save click — worse UX than this lighter nudge.
 async function openEntryForFix(entryId) {
-    await openSlideOver(entryId);
+    // Bail if the editor didn't actually switch (user cancelled the discard
+    // prompt): the steps below would unmask + select the password of whatever
+    // entry is still open, and pulse Generate on it — the wrong entry.
+    if (!(await openSlideOver(entryId))) return;
     const pwd = document.getElementById('soPassword');
     if (pwd) {
         pwd.type = 'text';       // unmask so the user sees what they're replacing