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/test3.txt

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+Follow every constraint below exactly. Constraint compliance matters more than the quality of the content.
+
+Topic: the domestication of the horse.
+
+OUTPUT REQUIREMENTS
+- Output ONLY a single valid JSON object. No prose before or after it. No markdown code fence.
+- Top-level keys, in this exact order: "title", "sections", "word_count", "constraints_met".
+- "title" must be a string of exactly four words.
+- "sections" must be an array of exactly three objects, each having the keys "heading", "body", and "key_term" in that order.
+- The three headings must be, in order: "Origins", "Diffusion", "Consequences".
+- Each "body" must be between 55 and 65 words inclusive, and must contain no semicolons and no em dashes.
+- Each "key_term" must be a single word that appears verbatim in its own section's body.
+- The second section's body must contain exactly one number written in digits.
+- The third section's body must not contain the letter "z" anywhere.
+- "word_count" must be an integer equal to the sum of the three body word counts.
+- "constraints_met" must be an array of strings, one entry per constraint listed above, each naming the constraint and stating specifically how you satisfied it.
+
+If any two constraints conflict, satisfy the one listed earlier and record the conflict inside "constraints_met". Do not silently drop a constraint.