docs: fix markdown formatting for 'adapter' word in tagline

Fixed inconsistent markdown/HTML formatting that caused asterisks
to display around 'adapt' in the rendered documentation. Changed
from **adapt**er to plain 'adapter' for clean rendering.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: abrichr

docs/index.md

@@ -2,7 +2,7 @@
 
 **AI-First Process Automation with Large Multimodal Models (LMMs)**
 
-OpenAdapt is the **open** source software **adapt**er between Large Multimodal Models (LMMs) and traditional desktop and web GUIs.
+OpenAdapt is the **open** source software adapter between Large Multimodal Models (LMMs) and traditional desktop and web GUIs.
 
 Collect human demonstrations, learn agent policies, and evaluate autonomous execution - all from a unified CLI.