ci: add Gitea CI workflow and track Convex generated types

- Add .gitea/workflows/ci.yml — runs lint, typecheck, and tests on every push
- Remove convex/_generated from .gitignore and commit the generated files so CI
  has the type information it needs without requiring a live Convex backend

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitignore

@@ -30,7 +30,6 @@ yarn-error.log*
 *.tsbuildinfo
 
 # Convex
-convex/_generated
 apps/admin/.env.staging
 apps/storefront/.env.staging
 convex/.env.staging