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>

plugin/openclaw.plugin.json

@@ -0,0 +1,21 @@
+{
+  "id": "prism-facet",
+  "name": "PrismFacet",
+  "version": "0.1.0",
+  "description": "Dynamic system prompt injection via routers and rules",
+  "main": "index.js",
+  "configSchema": {
+    "type": "object",
+    "additionalProperties": false,
+    "properties": {
+      "routersDir": {
+        "type": "string",
+        "description": "Directory containing router .ts/.js files (default: {pluginDir}/routers)"
+      },
+      "rulesFile": {
+        "type": "string",
+        "description": "Path to rules.json (default: {pluginDir}/rules.json)"
+      }
+    }
+  }
+}