fix(autofill): kill residual hotkey chord; dedicated fail-balloon setting

Residual new-entry trigger (1 in 6): password chars go out as
KEYEVENTF_UNICODE (VK_PACKET, can't match a hotkey) — the real chord risk is
the Ctrl+A clear-field, which sends a real VK_A. If the user re-presses
Ctrl+Shift mid-sequence, that VK_A becomes physical Ctrl+Shift+A = our own
new-entry hotkey. ForceReleaseModifiers now runs inside
SendSelectAllAndDelete, at the risky instant, not just once up front.

Balloon: was gated by "Show tray notifications" (OFF for this user) — now
gated by its own synced setting "Tray alert when autofill is blocked"
(autofillFailBalloon, Settings > Autofill, default ON), carried as notify=0
on cmd://autofill/execute. ShowBalloon no longer gates internally; each
caller applies its own setting.

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

index.html

@@ -642,6 +642,19 @@
                         <span class="toggle-slider"></span>
                     </label>
                 </div>
+                <div class="setting-row">
+                    <span>
+                        Tray alert when autofill is blocked
+                        <small class="setting-hint">
+                            Shows a Windows balloon if the fill fails while the
+                            app is hidden (e.g. the target runs as administrator).
+                        </small>
+                    </span>
+                    <label class="toggle">
+                        <input type="checkbox" id="settingAutofillFailBalloon">
+                        <span class="toggle-slider"></span>
+                    </label>
+                </div>
                 <div id="settingAutofillHotkeysRow" style="margin-top:8px">
                     <div class="setting-row">
                         <span style="font-size:12px;color:var(--text-dim)">