feat: implement vendor selfbot dependency modernization plan

- Update submodule `discord.js-selfbot-v13` to latest commit.
- Create implementation plan for modernizing the vendored dependency, focusing on toolchain replacement with Biome and runtime dependency auditing.
- Establish a design document outlining goals, scope, approach, toolchain design, runtime dependency design, and validation steps.
- Ensure public API compatibility and maintain existing functionality during modernization efforts.

biome.json

@@ -1,6 +1,6 @@
 {
   "files": {
-    "includes": ["src/**/*.ts", "tests/**/*.ts", "*.json", "*.ts"]
+    "includes": ["src/**/*.ts", "tests/**/*.ts", "*.json", "*.ts", "!vendor/**"]
   },
   "formatter": {
     "enabled": true,