refactor: reorganize examples directory with topic-based subdirectories

Reorganize examples directory into logical topic-based subdirectories with
comprehensive documentation:

- templates/: ISO/ARC42 documentation templates
- asset-management/: Asset management prototypes and demos
- essays/: Long-form content examples
- invoicing/: Invoice generation examples
- plugins/: Plugin development examples
- issue-demos/: Issue prevention demonstrations
- design-patterns/: Design pattern examples

Each subdirectory includes a README.txt file with topic description and
contributor signatures based on file creation timestamps.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

examples/asset-management/demo_workspace/shared_assets/images/25965aaacc4f361784870ed2624f0178ea7c3cf33961ffb73ef13bafed7cd28c.png

@@ -0,0 +1 @@
+PNG_IMAGE_CONTENT_LOGO

examples/asset-management/demo_workspace/shared_assets/images/54f88ec7aa8570d4ad655943d36f5db47021501baeac8ceeb3b726157de6ebf5.png

@@ -0,0 +1 @@
+PNG_IMAGE_CONTENT_DIAGRAM

examples/asset-management/demo_workspace/shared_assets/registry.json

@@ -0,0 +1,21 @@
+{
+  "assets": {
+    "25965aaacc4f361784870ed2624f0178ea7c3cf33961ffb73ef13bafed7cd28c": {
+      "original_name": "logo.png",
+      "size": 22,
+      "mime_type": "image/png",
+      "extension": ".png",
+      "created": "2025-10-08T01:50:01.099764",
+      "stored_path": "images/25965aaacc4f361784870ed2624f0178ea7c3cf33961ffb73ef13bafed7cd28c.png"
+    },
+    "54f88ec7aa8570d4ad655943d36f5db47021501baeac8ceeb3b726157de6ebf5": {
+      "original_name": "diagram.png",
+      "size": 25,
+      "mime_type": "image/png",
+      "extension": ".png",
+      "created": "2025-10-08T01:50:01.104199",
+      "stored_path": "images/54f88ec7aa8570d4ad655943d36f5db47021501baeac8ceeb3b726157de6ebf5.png"
+    }
+  },
+  "version": "1.0"
+}