feat: add `database-planetscale` module

[ronak-create]

Summary

Add PlanetScale as a database option — a serverless MySQL-compatible platform with a branch-based workflow.

Why

PlanetScale is a popular managed MySQL provider with its own serverless driver (@planetscale/database) that works in edge runtimes.
It pairs naturally with Hono and Cloudflare Workers.

---

Files to generate

• src/db/client.ts — PlanetScale connect() client
• .env.example — DATABASE_HOST, DATABASE_USERNAME, DATABASE_PASSWORD

---

Implementation hints

• Add packages/modules/src/database/planetscale.ts
  → closest analogue is mysql.ts

• Key dependency:

  • @planetscale/database

• No migration file needed
  (PlanetScale manages schema via branching — note this in a comment inside client.ts)

• Register in same places as other database modules

---

Contributor guidance

Refer to CONTRIBUTING.md → "Adding a New Module"

---

Acceptance criteria

• foundation create lists PlanetScale as a database option
• Generated client.ts type-checks cleanly
• Snapshot test added