fix: Resolve MkDocs build failures in strict mode (#976)

- Create missing docs/design/INDEX.md referenced in mkdocs.yml nav
- Fix nested code fences in landing-page-strategy.md causing sections 6
  and 7 to be rendered inside code blocks instead of as proper headings

The nested ```bash block inside section 5.5's outer ``` block was causing
parsing issues. Using 4 backticks for the outer block allows proper nesting.

Co-authored-by: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: abrichr

docs/design/INDEX.md

@@ -0,0 +1,11 @@
+# Design Documents
+
+This section contains design documents and specifications for OpenAdapt features and components.
+
+## Documents
+
+- [System Tray App](openadapt-tray.md) - Design specification for the OpenAdapt system tray application
+- [Tray Logging](tray-logging.md) - Logging architecture for the tray application
+- [Telemetry](telemetry-design.md) - Telemetry and analytics design
+- [Landing Page Strategy](landing-page-strategy.md) - Website landing page strategy and messaging
+- [Repo Rename Analysis](repo-rename-analysis.md) - Analysis for repository renaming considerations

docs/design/landing-page-strategy.md

@@ -371,7 +371,7 @@ No vendor lock-in, ever.
 
 ### 5.5 For Developers Section
 
-```
+````
 ## Built for Developers
 
 ### Modular Architecture
@@ -404,7 +404,7 @@ Integrated with Windows Agent Arena (WAA), WebArena, and OSWorld.
 Compare your models against published baselines.
 
 [View Documentation] [GitHub Repository]
-```
+````
 
 ### 5.6 For Enterprise Section