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>

package.json

@@ -2,10 +2,10 @@
   "name": "prism-facet",
   "version": "0.1.0",
   "type": "module",
-  "main": "dist/index.js",
   "scripts": {
-    "build": "tsc",
-    "watch": "tsc --watch"
+    "build": "tsc --project tsconfig.plugin.json",
+    "install-plugin": "node scripts/install.mjs --install",
+    "uninstall-plugin": "node scripts/install.mjs --uninstall"
   },
   "devDependencies": {
     "@types/node": "^25.6.0",