Add Mermaid diagram support and update architecture documentation

- Included a new JavaScript file for Mermaid configuration to ensure consistent diagram sizing across documentation.
- Enhanced architecture documentation to reflect the updated pipeline engine structure, including VAD, ASR, TD, LLM, and TTS components.
- Updated various sections to clarify the integration of external services and tools within the architecture.
- Improved styling for Mermaid diagrams to enhance visual consistency and usability.

docs/content/stylesheets/extra.css

@@ -83,9 +83,13 @@
   border: none;
 }
 
-/* Mermaid Diagram Styling */
+/* Mermaid Diagram Styling - consistent element size across diagrams */
 .mermaid {
   margin: 1.5rem 0;
+  overflow-x: auto;
+}
+.mermaid svg {
+  min-width: min-content;
 }
 
 /* Navigation Enhancement */