feat(assets): standardize asset configuration with capacitor-assets

- Replace manual ImageMagick scripts with official capacitor-assets toolchain
- Consolidate duplicate asset sources to single resources/ directory
- Implement comprehensive asset configuration schema and validation
- Add CI safeguards for asset validation and platform asset detection
- Convert capacitor.config.json to TypeScript format
- Pin Node.js version for deterministic builds
- Remove legacy manual asset generation scripts:
  * generate-icons.sh, generate-ios-assets.sh, generate-android-icons.sh
  * check-android-resources.sh, check-ios-resources.sh
  * purge-generated-assets.sh
- Add new asset management commands:
  * assets:config - generate/update configurations
  * assets:validate - validate configurations
  * assets:clean - clean generated assets (dev only)
  * build:native - build with asset generation
- Create GitHub Actions workflow for asset validation
- Update documentation with new asset management workflow

This standardization eliminates asset duplication, improves build reliability,
and provides a maintainable asset management system using Capacitor defaults.

Breaking Changes: Manual asset generation scripts removed
Migration: Assets now sourced from resources/ directory only
CI: Automated validation prevents committed platform assets

config/assets/capacitor-assets.config.json

@@ -0,0 +1,32 @@
+{
+  "icon": {
+    "source": "resources/icon.png",
+    "android": {
+      "adaptive": {
+        "foreground": "resources/icon.png",
+        "background": "#121212",
+        "monochrome": "resources/icon.png"
+      },
+      "target": "android/app/src/main/res"
+    },
+    "ios": {
+      "padding": 0,
+      "target": "ios/App/App/Assets.xcassets/AppIcon.appiconset"
+    },
+    "web": {
+      "target": "public/img/icons"
+    }
+  },
+  "splash": {
+    "source": "resources/splash.png",
+    "darkSource": "resources/splash_dark.png",
+    "android": {
+      "scale": "cover",
+      "target": "android/app/src/main/res"
+    },
+    "ios": {
+      "useStoryBoard": true,
+      "target": "ios/App/App/Assets.xcassets"
+    }
+  }
+}