Update release version to v0.1.2.b and refactor terminal.py for improved functionality

- Updated the release version in index.html and version.txt to v0.1.2.b.
- Refactored terminal.py to consolidate system detection and plugin management functionalities, enhancing code organization and maintainability.
- Removed deprecated modules and streamlined the command execution process for better performance.

index.html

@@ -46,7 +46,7 @@
     <div class="hero__metrics">
       <div class="metric">
         <p class="metric__label">Current release</p>
-        <p class="metric__value">v0.1.2.a.9</p>
+        <p class="metric__value">v0.1.2.b</p>
       </div>
       <div class="metric">
         <p class="metric__label">Supported families</p>