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/context-knowledge/suite.json

@@ -0,0 +1,5 @@
+{
+  "name": "Context & Knowledge",
+  "description": "Handling large inputs and staying grounded: long-context recall, retrieval from provided sources, strict instruction following and persona consistency.",
+  "order": 40
+}