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>

android/nix-android-sdk/android-studio-devbox-config.sh

@@ -0,0 +1,59 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+SCRIPT_DIR="$(cd -- "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+PROJECT_DIR="$(cd -- "$SCRIPT_DIR/../.." && pwd)"
+IDEA_DIR="$PROJECT_DIR/.idea"
+LIBRARIES_DIR="$IDEA_DIR/libraries"
+FLUTTER_SDK="$PROJECT_DIR/.devbox/nix/profile/default"
+DART_SDK="$FLUTTER_SDK/bin/cache/dart-sdk"
+
+mkdir -p "$IDEA_DIR"
+if [ ! -x "$FLUTTER_SDK/bin/flutter" ]; then
+  echo "Flutter not found at $FLUTTER_SDK/bin/flutter. Run devbox install to download it." >&2
+  exit 1
+fi
+
+if [ ! -d "$DART_SDK" ]; then
+  echo "Dart SDK not found at $DART_SDK. Run flutter doctor to populate the cache." >&2
+  exit 1
+fi
+
+mkdir -p "$LIBRARIES_DIR"
+
+cat > "$IDEA_DIR/flutter.xml" <<'EOF'
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="FlutterSdkSettings">
+    <option name="FLUTTER_SDK_PATH" value="$PROJECT_DIR$/.devbox/nix/profile/default" />
+  </component>
+</project>
+EOF
+
+cat > "$IDEA_DIR/dart.xml" <<'EOF'
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="DartSdkGlobalLibSettings">
+    <option name="dartSdkPath" value="$PROJECT_DIR$/.devbox/nix/profile/default/bin/cache/dart-sdk" />
+  </component>
+</project>
+EOF
+
+dart_libs=$(find "$DART_SDK/lib" -maxdepth 1 -mindepth 1 -type d -printf '%f\n' | sort)
+tmp_file=$(mktemp)
+{
+  echo '<component name="libraryTable">'
+  echo '  <library name="Dart SDK">'
+  echo '    <CLASSES>'
+  for lib in $dart_libs; do
+    printf '      <root url="file://$PROJECT_DIR$/.devbox/nix/profile/default/bin/cache/dart-sdk/lib/%s" />\n' "$lib"
+  done
+  echo '    </CLASSES>'
+  echo '    <JAVADOC />'
+  echo '    <SOURCES />'
+  echo '  </library>'
+  echo '</component>'
+} > "$tmp_file"
+mv "$tmp_file" "$LIBRARIES_DIR/Dart_SDK.xml"
+
+echo "Android Studio configured. Flutter SDK: $FLUTTER_SDK"