Add ImageField component and client-side upload script

src/components/admin/ImageField.astro

@@ -0,0 +1,28 @@
+---
+interface Props {
+  name: string;
+  label: string;
+  value?: string | null;
+  scope: "settings" | "cases" | "posts";
+  id?: string;
+}
+
+const { name, label, value = "", scope, id = name } = Astro.props;
+---
+
+<div class="image-field" data-image-field data-scope={scope}>
+  <label for={id}>{label}</label>
+  <input
+    id={id}
+    name={name}
+    type="text"
+    value={value ?? ""}
+    placeholder="https://... 或按下面上傳"
+    class="image-url"
+  />
+  <div class="image-actions">
+    <input type="file" accept="image/*" data-image-input />
+    <span class="image-status" data-image-status></span>
+  </div>
+  <img class="image-preview" data-image-preview src={value || undefined} alt="" hidden={!value} />
+</div>

src/layouts/AdminLayout.astro

@@ -49,6 +49,73 @@ const isActive = (href: string) =>
     <main class="inner">
       <slot />
     </main>
+    <script>
+      const MAX_WIDTH = 1600;
+      const QUALITY = 0.85;
+
+      async function toOptimised(file: File): Promise<Blob> {
+        if (!("createImageBitmap" in window)) return file;
+        try {
+          const bitmap = await createImageBitmap(file);
+          const scale = Math.min(1, MAX_WIDTH / bitmap.width);
+          const width = Math.max(1, Math.round(bitmap.width * scale));
+          const height = Math.max(1, Math.round(bitmap.height * scale));
+          const canvas = document.createElement("canvas");
+          canvas.width = width;
+          canvas.height = height;
+          const ctx = canvas.getContext("2d");
+          if (!ctx) return file;
+          ctx.drawImage(bitmap, 0, 0, width, height);
+          if (typeof bitmap.close === "function") bitmap.close();
+          const blob = await new Promise<Blob | null>((resolve) =>
+            canvas.toBlob(resolve, "image/webp", QUALITY),
+          );
+          return blob ?? file;
+        } catch {
+          return file;
+        }
+      }
+
+      async function upload(field: HTMLElement, file: File): Promise<void> {
+        const scope = field.dataset.scope ?? "";
+        const input = field.querySelector<HTMLInputElement>(".image-url");
+        const preview = field.querySelector<HTMLImageElement>(".image-preview");
+        const status = field.querySelector<HTMLElement>(".image-status");
+        if (!input || !status) return;
+
+        status.textContent = "上傳中…";
+        const blob = await toOptimised(file);
+        const body = new FormData();
+        body.append("file", new File([blob], file.name, { type: blob.type }));
+        body.append("scope", scope);
+
+        try {
+          const res = await fetch("/admin/upload", { method: "POST", body });
+          const data = (await res.json()) as { ok: boolean; url?: string; error?: string };
+          if (!res.ok || !data.ok || !data.url) {
+            status.textContent = data.error ?? "上傳失敗。";
+            return;
+          }
+          input.value = data.url;
+          if (preview) {
+            preview.src = data.url;
+            preview.hidden = false;
+          }
+          status.textContent = "✓ 已上傳";
+        } catch {
+          status.textContent = "上傳失敗，請檢查網絡。";
+        }
+      }
+
+      document.querySelectorAll<HTMLElement>("[data-image-field]").forEach((field) => {
+        const fileInput = field.querySelector<HTMLInputElement>("[data-image-input]");
+        if (!fileInput) return;
+        fileInput.addEventListener("change", () => {
+          const file = fileInput.files?.[0];
+          if (file) void upload(field, file);
+        });
+      });
+    </script>
   </body>
 </html>
 
@@ -114,5 +181,11 @@ const isActive = (href: string) =>
   .err { color: #a32d2d; font-size: 13px; font-weight: 600; }
   .grid2 { display: grid; grid-template-columns: 1fr 1fr; gap: 16px; }
   @media (max-width: 640px) { .grid2 { grid-template-columns: 1fr; } }
+  .image-field { display: block; }
+  .image-actions { display: flex; align-items: center; gap: 10px; margin-top: 8px; flex-wrap: wrap; }
+  .image-actions input[type="file"] { font: inherit; font-size: 13px; max-width: 100%; }
+  .image-status { font-size: 12.5px; font-weight: 600; color: #0b8a5e; }
+  .image-preview { display: block; margin-top: 10px; max-width: 220px; border-radius: 10px; }
+  .image-preview[hidden] { display: none; }
   .row { display: grid; gap: 12px; grid-template-columns: 1fr; }
 </style>