feat: add intentional reader routes

src/features/posts/components/user-form.tsx

@@ -0,0 +1,47 @@
+import { type FormEvent, useState } from 'react'
+import { normalizeUserTarget } from '../inputs'
+
+type Props = {
+  initialTarget: string
+  onSubmit: (target: string) => void
+}
+
+export function UserForm({ initialTarget, onSubmit }: Props) {
+  const [target, setTarget] = useState(initialTarget)
+  const [error, setError] = useState('')
+  const submit = (event: FormEvent) => {
+    event.preventDefault()
+    try {
+      const handle = normalizeUserTarget(target)
+      setError('')
+      onSubmit(handle)
+    } catch (cause) {
+      setError(
+        cause instanceof Error ? cause.message : '入力内容を確認してください。',
+      )
+    }
+  }
+
+  return (
+    <form className="intent-form" onSubmit={submit}>
+      <label className="field">
+        <span>ハンドルまたはプロフィール URL</span>
+        <input
+          autoComplete="off"
+          aria-describedby={error ? 'target-error' : undefined}
+          aria-invalid={Boolean(error)}
+          name="target"
+          value={target}
+          onChange={(event) => setTarget(event.currentTarget.value)}
+          placeholder="@handle または https://x.com/handle"
+        />
+        {error ? (
+          <span className="field-error" id="target-error" role="alert">
+            {error}
+          </span>
+        ) : null}
+      </label>
+      <button type="submit">表示</button>
+    </form>
+  )
+}