docs(stacks): use type-only import for AppType

[o8n]

Same as #622 and #744, applied to docs/concepts/stacks.md.

Both AppType imports in this page are only used as a type parameter to hc<>(), so they should be type-only imports. With verbatimModuleSyntax: true, the current example fails to compile with TS1484.

Reproduction

Node.js v22.12.0, TypeScript 6.0.3, Hono 4.12.18.

tsconfig.json

{
  "compilerOptions": {
    "target": "ESNext",
    "module": "ESNext",
    "moduleResolution": "Bundler",
    "strict": true,
    "verbatimModuleSyntax": true,
    "skipLibCheck": true,
    "noEmit": true
  }
}

tsc --noEmit on the current example in docs/concepts/stacks.md

client.ts:1:10 - error TS1484: 'AppType' is a type and must be imported using a type-only import when 'verbatimModuleSyntax' is enabled.

1 import { AppType } from './server'
           ~~~~~~~


Found 1 error in client.ts:1

After applying this PR, tsc --noEmit exits cleanly with no output.

Happy to adjust if anything is off.

[yusukebe]

LGTM!

[yusukebe]

@o8n

Nice! Thanks.