chore(tooling): add knip configuration to detect unused files, dependencies and exports across the monorepo

[sundaram2021]

Is your feature request related to a problem? Please describe.

knip is already listed as a root devDependency ("knip": "^6.22.0" in package.json), but there is no Knip configuration file or script anywhere in the repo, so the tool is currently unusable. With 11 apps (apps/) and 23 packages (packages/) in this Turborepo workspace, unused files, dependencies, and exports accumulate silently over time — there is no automated way to detect them.

Describe the solution you'd like

Add a Knip configuration tailored to this monorepo:

• A knip.json (or equivalent config) at the repo root defining:
  • Workspaces for all entries under apps/* and packages/*
  • Entry points matching our conventions (Next.js app router for dashboard/docs, Elysia entry files for api/basket, Drizzle schemas/configs, tracker/SDK build outputs, test files, etc.)
  • Ignore patterns for generated code, config files, and intentionally-kept exports
• A root script (e.g., "knip": "knip") so it can be run locally via bun run knip
• Optionally wire it into CI alongside lint / check-types

This gives us a single command to surface unused dependencies, exports, files, and duplicate configs across every workspace.

Describe alternatives you've considered

• Running npx/bunx knip ad hoc without committed config — results would be noisy and non-reproducible across contributors.
• Alternative tools like depcheck or ts-prune — they cover only parts of what Knip does (no monorepo workspace support, no unused-file detection) and are less maintained.

Additional context

• Knip v6 is already pinned in root devDependencies, so no new dependency is needed — only configuration and wiring.
• Should play nicely with existing tooling: Bun workspaces, Turborepo task graph, Biome/Ultracite lint setup, and the catalog: dependency protocol in package.json.