build: Android's built-in Kotlin, the three plugins applying KGP themselves patched in third_party/

AGP 9 compiles Kotlin itself (android.builtInKotlin=true in every app),
and warns that applying the Kotlin Gradle Plugin will soon fail.
flutter_web_auth_2 5.1.0, keyboard_height_plugin 0.3.0 and flutter_tts
4.2.5 still apply it unconditionally, so their pub releases are copied
into third_party/ with only their android/build.gradle changed, and
the root overrides them by path (third_party/README.md says when to
drop each). The servers' images copy third_party/, as pub refuses an
override whose path is missing. third_party/ isn't our own code: left
out of the analysis and the format check.

All four apps' APKs build without the warning. A Kotlin daemon's
session file that slipped into Train's android/ goes, and every app's
android/.gitignore keeps .kotlin/ out.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

pubspec.lock

@@ -807,20 +807,18 @@ packages:
     source: sdk
     version: "0.0.0"
   flutter_tts:
-    dependency: transitive
+    dependency: "direct overridden"
     description:
-      name: flutter_tts
-      sha256: ce5eb209b40e95f2f4a1397116c87ab2fcdff32257d04ed7a764e75894c03775
-      url: "https://pub.dev"
-    source: hosted
+      path: "third_party/flutter_tts"
+      relative: true
+    source: path
     version: "4.2.5"
   flutter_web_auth_2:
-    dependency: transitive
+    dependency: "direct overridden"
     description:
-      name: flutter_web_auth_2
-      sha256: a7655829251ee63aae64a748f8512f36670d8eba4657b0055cdf5ef304a9d164
-      url: "https://pub.dev"
-    source: hosted
+      path: "third_party/flutter_web_auth_2"
+      relative: true
+    source: path
     version: "5.1.0"
   flutter_web_auth_2_platform_interface:
     dependency: transitive
@@ -1142,12 +1140,11 @@ packages:
     source: hosted
     version: "4.12.0"
   keyboard_height_plugin:
-    dependency: transitive
+    dependency: "direct overridden"
     description:
-      name: keyboard_height_plugin
-      sha256: d57944cd3e4f8d9cb4adb1b7f1300d14a8dcec99bfb4414d78c7dd0120c1d66c
-      url: "https://pub.dev"
-    source: hosted
+      path: "third_party/keyboard_height_plugin"
+      relative: true
+    source: path
     version: "0.3.0"
   latlong2:
     dependency: transitive