feat: implement selfbot workspace submodule

- Add `discord.js-selfbot-v13` as a git submodule in `vendor/`
- Update `pnpm-workspace.yaml` to include the new submodule path
- Modify `.gitmodules` to track the submodule repository
- Change `discord.js-selfbot-v13` dependency in `package.json` to use `workspace:*`
- Create implementation and design documents for the submodule integration

docs/superpowers/specs/2026-05-15-selfbot-workspace-submodule-design.md

@@ -0,0 +1,24 @@
+# Selfbot Workspace Submodule Design
+
+## Goal
+
+Replace the npm-resolved `discord.js-selfbot-v13` dependency with a custom repository checked into this project as a git submodule and consumed through pnpm workspace resolution.
+
+## Approach
+
+Use `vendor/discord.js-selfbot-v13` as the submodule path. Initialize it from `https://github.com/aiko-chan-ai/discord.js-selfbot-v13.git`, then change the submodule repository `origin` remote to `ssh://git@43.134.105.109:22222/exceed/discord.js-selfbot.git`.
+
+Configure pnpm workspaces so the root project and the vendored package are both workspace packages. Change the root dependency from the npm version range to `workspace:*`, forcing pnpm to resolve `discord.js-selfbot-v13` from the submodule package.
+
+## Files to Change
+
+- `.gitmodules`: track the new submodule path and URL.
+- `pnpm-workspace.yaml`: include the root package and `vendor/discord.js-selfbot-v13`.
+- `package.json`: change `discord.js-selfbot-v13` to `workspace:*`.
+- `pnpm-lock.yaml`: refresh dependency resolution after the workspace change.
+
+## Validation
+
+After the submodule and dependency changes, run `pnpm install` to update the workspace lockfile and links, then run `pnpm run typecheck` to confirm the app still resolves the selfbot package.
+
+If the vendored package requires a build step before TypeScript can resolve it, use that package's own scripts and rerun root validation.