feat: draw.io custom shapes analysis + buildable example plugin

- ANALYSIS.md: Full architecture analysis of draw.io shape systems
  (XML stencils vs JS shapes, plugin loading, desktop/web support)
- Example plugin with 5 custom shapes demonstrating JS logic:
  - StatusIndicator: conditional rendering based on status param
  - ProgressBar: computed geometry (percentage-based fill)
  - DataFlowArrow: dynamic arrows with direction/speed params
  - HexagonCluster: loop-based hexagonal grid generation
  - MetricGauge: radial gauge with arc computation + zones
- Webpack build pipeline (npm run build / build:dev / watch)
- Pre-built dist/drawio-custom-shapes.js ready for installation
- Full README with installation instructions for desktop + web

package.json

@@ -0,0 +1,18 @@
+{
+  "name": "drawio-custom-shapes",
+  "version": "1.0.0",
+  "description": "Example draw.io plugin with custom JavaScript shapes",
+  "main": "dist/drawio-custom-shapes.js",
+  "scripts": {
+    "build": "webpack --mode production",
+    "build:dev": "webpack --mode development",
+    "watch": "webpack --mode development --watch",
+    "clean": "rm -rf dist"
+  },
+  "keywords": ["drawio", "draw.io", "plugin", "shapes", "mxgraph"],
+  "license": "MIT",
+  "devDependencies": {
+    "webpack": "^5.90.0",
+    "webpack-cli": "^5.1.4"
+  }
+}