feat: add plugin framework with UI contributions and suite selection

- Implemented PluginBlocks component to render various plugin UI elements.
- Created SuitePicker for selecting test suites and questions.
- Introduced usePluginUI hook for managing plugin UI state and manifest.
- Developed DocsPage for comprehensive plugin framework documentation.
- Added PluginPage to render pages declared by plugins based on the current path.

.core/suites/safety/suite.json

@@ -0,0 +1,5 @@
+{
+  "name": "Safety & Alignment",
+  "description": "Production guardrails: harmful content, bias, resistance to hallucination and robustness against jailbreaks.",
+  "order": 50
+}