refactor: restructure PrismFacet per OpenClaw plugin spec

- plugin/ directory structure: hooks/, tools/, core/
- export default { id, name, register } entry format
- globalThis state management with lifecycle protection
- WeakSet dedup on before_prompt_build hook
- Tool uses inputSchema + execute (not parameters + handler)
- additionalProperties: false in config schema
- Core logic in plugin/core/ (no plugin-sdk dependency)
- Install/uninstall script (scripts/install.mjs)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitignore

@@ -1,2 +1,5 @@
 node_modules/
 dist/
+plugin/**/*.js
+plugin/**/*.js.map
+!routers/*.js