chore: refactor workflows & deploy playground

[sagar-kap]

Description

Fix the broken CI, link the playground via workspace ref, and add GitHub Pages deployment.

Modifications

• Rename ci.yml → qa.yml; use pnpm/action-setup@v4 with pinned pnpm 11.1.3 and
  Node 22. Adds test:types and prepack to CI.
• Rename playground package and switch to @weburz/particle-canvas: workspace:*, so
  it resolves the module via the package name (same path real consumers will use).
• Add nitro.preset: 'github_pages' and env-driven app.baseURL to
  playground/nuxt.config.ts.
• Add deploy-playground.yml to publish the playground to GitHub Pages on every merge
  to main.
• Add issue templates and a pull-request template under .github/.

Fixed issue(s):

N/A