devbox setup, dep upgrades, lint fixes, Android build fixes

- Add devbox.json pinning Flutter 3.35.7, Android SDK (Nix flake),
  openjdk17, just, openssl
- Add android/nix-android-sdk/ Nix flake + flake.lock + Android Studio
  config script
- Add justfile with build/get/upgrade/icons/analyze/rebuild recipes
- flutter pub upgrade --major-versions: file_picker ^11, google_fonts ^8,
  permission_handler ^12, share_plus ^12, flutter_lints ^6 (+71 transitive)
- Fix file_picker v11 API: FilePicker.platform → FilePicker.getDirectoryPath()
- Fix all 37 analyzer issues: deprecated APIs (window, WillPopScope, Share,
  SvgPicture color), async BuildContext guards, key constructors, private
  createState() return types, unused locals, print → debugPrint, etc.
- Hook _handleCommand into onSubmitted for : prefix commands
- Android: Gradle 8.3→8.11.1, AGP 8.2.2→8.9.1, KGP 1.8.22→2.2.20,
  compileSdk/targetSdk 34→36, namespace auto-derivation for library modules,
  kotlin.compiler.execution.strategy=in-process

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

devbox.json

@@ -0,0 +1,32 @@
+{
+  "$schema": "https://raw.githubusercontent.com/jetify-com/devbox/main/packages/devbox.schema.json",
+  "packages": [
+    "nixpkgs#git",
+    "path:./android/nix-android-sdk#android-sdk",
+    "nixpkgs#android-tools",
+    "nixpkgs#openjdk17",
+    "just@latest",
+    "openssl@latest",
+    "flutter@3.35.7-sdk-links"
+  ],
+  "env": {
+    "ANDROID_SDK_ROOT": "$DEVBOX_PACKAGES_DIR/share/android-sdk",
+    "ANDROID_HOME": "$DEVBOX_PACKAGES_DIR/share/android-sdk"
+  },
+  "nix_config": {
+    "allow-unfree": "true"
+  },
+  "shell": {
+    "init_hook": [
+      "flutter --version",
+      "if command -v android >/dev/null 2>&1; then export ANDROID_HOME=$(command -v android | sed -E 's|(.*libexec/android-sdk).*|\\1|'); fi",
+      "if [ -n \"$ANDROID_HOME\" ]; then export PATH=$ANDROID_HOME/cmdline-tools/latest/bin:$PATH; fi"
+    ],
+    "scripts": {
+      "doctor": "flutter doctor -v",
+      "link-android-tools": "if [ -n \"$ANDROID_HOME\" ] && [ ! -d \"$ANDROID_HOME/cmdline-tools/latest\" ] && [ -d \"$ANDROID_HOME/cmdline-tools/8.0\" ]; then ln -s \"$ANDROID_HOME/cmdline-tools/8.0\" \"$ANDROID_HOME/cmdline-tools/latest\"; fi",
+      "studio-config": "./android/nix-android-sdk/android-studio-devbox-config.sh",
+      "studio": "PROJECT_DIR=${DEVBOX_PROJECT_ROOT:-$(pwd)}; if command -v android-studio >/dev/null 2>&1; then android-studio \"$PROJECT_DIR\" >/dev/null 2>&1 &\nelif [ -x \"$HOME/.local/share/JetBrains/Toolbox/apps/android-studio/bin/studio.sh\" ]; then \"$HOME/.local/share/JetBrains/Toolbox/apps/android-studio/bin/studio.sh\" \"$PROJECT_DIR\" >/dev/null 2>&1 &\nelse echo \"Android Studio not found. Install it via JetBrains Toolbox.\" >&2; exit 1; fi"
+    }
+  }
+}