Create "Apps" section in documentation and Add interactive c4a-script playground and LLM context builder for Crawl4AI

- Created a new HTML page (`index.html`) for the interactive LLM context builder, allowing users to select and combine different `crawl4ai` context files.
- Implemented JavaScript functionality (`llmtxt.js`) to manage component selection, context types, and file downloads.
- Added CSS styles (`llmtxt.css`) for a terminal-themed UI.
- Introduced a new Markdown file (`build.md`) detailing the requirements and functionality of the context builder.
- Updated the navigation in `mkdocs.yml` to include links to the new context builder and demo apps.
- Added a new Markdown file (`why.md`) explaining the motivation behind the new context structure and its benefits for AI coding assistants.

docs/md_v2/apps/c4a-script/blockly-demo.c4a

@@ -0,0 +1,21 @@
+# Demo: Login Flow with Blockly
+# This script can be created visually using Blockly blocks
+
+GO https://example.com/login
+WAIT `#login-form` 5
+
+# Check if already logged in
+IF (EXISTS `.user-avatar`) THEN GO https://example.com/dashboard
+
+# Fill login form
+CLICK `#email`
+TYPE "demo@example.com"
+CLICK `#password`
+TYPE "password123"
+
+# Submit form
+CLICK `button[type="submit"]`
+WAIT `.dashboard` 10
+
+# Success message
+EVAL `console.log('Login successful!')`