feat: switch accent to Plum, finalize vault-door app icon, group filter Clear button

- Replace Copper accent with Plum (light #6B4577 / dark #A67FB0) across the main
  app and AutoFill extension.
- Replace the padlock app icon with a vault-door design (ring, hub, locking
  handle) in Plum, plus all macOS sizes.
- Add an AppIconImage asset (separate from the AppIcon icon-set, which SwiftUI
  can't reference directly at runtime) and show it on the unlock screen instead
  of a generic SF Symbol.
- GroupFilterView: move "Clear Filter" out of the list and into a leading
  toolbar button ("Clear", disabled when no filter is active), mirroring the
  trailing "Done" button.

KeeVault.xcodeproj/xcuserdata/kriss.xcuserdatad/xcschemes/xcschememanagement.plist

@@ -7,7 +7,7 @@
 		<key>AutoFill.xcscheme_^#shared#^_</key>
 		<dict>
 			<key>orderHint</key>
-			<integer>0</integer>
+			<integer>2</integer>
 		</dict>
 		<key>KeeVault.xcscheme_^#shared#^_</key>
 		<dict>