Hide Mail integration behind a kill switch pending the macOS 27 beta fix

Confirmed via live debugging this is a genuine OS bug (first-time
Automation consent grants never work on this beta), not fixable in-app.
Rather than ship a Settings section that can't currently work, added
MailTools.isHiddenPendingAppleFix (true for now) mirroring the existing
PersonalDataTools kill switch used for the same purpose during an earlier
Calendar/Contacts TCC bug — hides the Settings UI and forces mailEnabled
to false regardless of the persisted value, with no code deleted. Flip
back to false once a newer beta/RC is confirmed to fix it.

oAI/Services/SettingsService.swift

@@ -32,6 +32,15 @@ enum PersonalDataTools {
     static let isHiddenPendingAppleFix = false
 }
 
+/// Kill switch for the Mail integration, hidden while blocked by a confirmed macOS 27 beta bug:
+/// first-time Automation consent grants never show a dialog or create a TCC record at all (not
+/// fixable in-app — see feature_mail_applescript_integration in memory for the full investigation).
+/// Same shape as `PersonalDataTools` above. Flip back to `false` once Rune confirms a newer beta/RC
+/// fixes it — the tool code itself is complete and doesn't need changes, just re-enabling.
+enum MailTools {
+    static let isHiddenPendingAppleFix = true
+}
+
 @Observable
 class SettingsService {
     static let shared = SettingsService()
@@ -760,7 +769,7 @@ class SettingsService {
     // MARK: - Mail Settings (Apple Mail.app via AppleScript)
 
     var mailEnabled: Bool {
-        get { cache["mailEnabled"] == "true" }
+        get { !MailTools.isHiddenPendingAppleFix && cache["mailEnabled"] == "true" }
         set {
             cache["mailEnabled"] = String(newValue)
             DatabaseService.shared.setSetting(key: "mailEnabled", value: String(newValue))