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/manifest.json

@@ -0,0 +1,35 @@
+{
+  "id": "fusion-plugin-settings-demo",
+  "name": "Settings Demo Plugin",
+  "version": "0.1.0",
+  "description": "Example plugin demonstrating settings schema, hooks, and tools",
+  "author": "Fusion Team",
+  "homepage": "https://github.com/gsxdsm/fusion",
+  "settingsSchema": {
+    "greetingMessage": {
+      "type": "string",
+      "label": "Greeting Message",
+      "description": "Custom greeting message shown when the plugin loads",
+      "defaultValue": "Hello from Settings Demo!"
+    },
+    "maxTags": {
+      "type": "number",
+      "label": "Max Tags",
+      "description": "Maximum number of tags to suggest per task",
+      "defaultValue": 3
+    },
+    "enableLogging": {
+      "type": "boolean",
+      "label": "Enable Logging",
+      "description": "Log plugin activity to the console",
+      "defaultValue": true
+    },
+    "logLevel": {
+      "type": "enum",
+      "label": "Log Level",
+      "description": "Minimum log level to output",
+      "enumValues": ["debug", "info", "warn", "error"],
+      "defaultValue": "info"
+    }
+  }
+}