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/scripts/02-login-flow.c4a

@@ -0,0 +1,27 @@
+# Complete Login Flow
+# Demonstrates form interaction and authentication
+
+# Click login button
+CLICK `#login-btn`
+
+# Wait for login modal
+WAIT `.login-form` 3
+
+# Fill in credentials
+CLICK `#email`
+TYPE "demo@example.com"
+
+CLICK `#password`
+TYPE "demo123"
+
+# Check remember me
+IF (EXISTS `#remember-me`) THEN CLICK `#remember-me`
+
+# Submit form
+CLICK `button[type="submit"]`
+
+# Wait for success
+WAIT `.welcome-message` 5
+
+# Verify login succeeded
+IF (EXISTS `.user-info`) THEN EVAL `console.log('✅ Login successful!')`