fix: remove filePath getter that conflicts with Indiekit plugin loader

Indiekit's getInstalledPlugins() assigns plugin.filePath via require.resolve().
Our getter made the property read-only, causing:
  TypeError: Cannot set property filePath which has only a getter

Let Indiekit set it instead.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

index.js

@@ -1,5 +1,3 @@
-import path from "node:path";
-
 import express from "express";
 
 import { handleWebFinger } from "./lib/webfinger.js";
@@ -50,9 +48,7 @@ export default class ActivityPubEndpoint {
     };
   }
 
-  get filePath() {
+  // filePath is set by Indiekit's plugin loader via require.resolve()
-    return path.dirname(new URL(import.meta.url).pathname);
-  }
 
   /**
    * WebFinger routes — mounted at /.well-known/

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@rmdes/indiekit-endpoint-activitypub",
-  "version": "0.1.0",
+  "version": "0.1.1",
   "description": "ActivityPub federation endpoint for Indiekit via Fedify. Adds full fediverse support: actor, inbox, outbox, followers, following, syndication, and Mastodon migration.",
   "keywords": [
     "indiekit",