feat(FN-1469): create settings-loadable example plugin

- Add fusion-plugin-settings-demo package with settings schema (string, number, boolean, enum types)
- Add lifecycle hooks (onLoad, onTaskCreated, onTaskCompleted)
- Add tools (suggest_tags, status) with settings-driven behavior
- Add comprehensive tests with 24 test cases
- Add manifest.json for plugin metadata and README with Settings installation flow
- Update PLUGIN_AUTHORING.md with new example and install instructions
- Also includes: FN-1468 plugin wiring, FN-1456 abandon flow, FN-1429 always-green tests, FN-1440 Authentication in Settings, FN-1133 plugin hot-reload support

plugins/examples/fusion-plugin-settings-demo/tsconfig.json

@@ -0,0 +1,9 @@
+{
+  "extends": "../../tsconfig.base.json",
+  "compilerOptions": {
+    "outDir": "dist",
+    "rootDir": "src",
+    "types": ["node", "vitest/globals"]
+  },
+  "include": ["src/**/*"]
+}