chore: remove unused ticketing-example test fixture

[ocavue]

Summary

• Removes packages/db/test/fixtures/ticketing-example, a demo app that has lived under the db test fixtures since the integration was introduced (Introduce the db integration (prerelease) #10201, Jan 2024) but was never referenced by any .test.ts/.test.js.
• Drops the deprecated simple-stack-form dependency. This resolves a peer dep warn:

Before:

$ pnpm --version
11.0.9
$ pnpm peers check
Issues with peer dependencies found

✕ unmet peer zod
  Installed: 4.3.6
  Wanted:
    ^3.22.4:
      simple-stack-form@0.1.12

✕ unmet peer @cloudflare/workers-types
  Installed: 4.20260228.0
  Wanted:
    ^4.20260415.1:
      wrangler@4.83.0

After:

$ pnpm --version
11.0.9
$ pnpm peers check
Issues with peer dependencies found

✕ unmet peer @cloudflare/workers-types
  Installed: 4.20260228.0
  Wanted:
    ^4.20260415.1:
      wrangler@4.83.0

Test

CI should pass

Docs

N/A

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Latest commit: ceb43e7

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