feat: avatar upload via presigned PUT URL flow

- Go scraper: add PresignAvatarUploadURL/PresignAvatarURL/DeleteAvatar to
  Store interface, implement on HybridStore+MinioClient, register
  GET /api/presign/avatar-upload/{userId} and /api/presign/avatar/{userId}
- SvelteKit: replace direct AWS S3 SDK in minio.ts with presign calls to
  the Go scraper; rewrite avatar +server.ts (POST=presign, PATCH=record key)
- iOS: rewrite uploadAvatar() as 3-step presigned PUT flow; refactor
  chip components into shared ChipButton in CommonViews.swift

ui/src/routes/api/profile/avatar/+server.ts

@@ -1,62 +1,76 @@
 import { json, error } from '@sveltejs/kit';
 import type { RequestHandler } from './$types';
-import { putAvatar, presignAvatarUrl } from '$lib/server/minio';
+import { presignAvatarUploadUrl, presignAvatarUrl } from '$lib/server/minio';
 import { updateUserAvatarUrl, getUserByUsername } from '$lib/server/pocketbase';
 
-const MAX_SIZE = 5 * 1024 * 1024; // 5 MB
-const ALLOWED_TYPES = ['image/jpeg', 'image/png', 'image/webp', 'image/gif'];
+const ALLOWED_TYPES = ['image/jpeg', 'image/png', 'image/webp'];
 
 /**
  * POST /api/profile/avatar
- * Accepts multipart/form-data with a "file" field.
- * Uploads to MinIO libnovel-avatars bucket, stores the key in app_users.avatar_url.
- * Returns { avatar_url: <presigned-url> }.
+ * Body: JSON { mime_type: "image/jpeg" | "image/png" | "image/webp" }
+ *
+ * Returns a short-lived presigned PUT URL pointing at MinIO (public endpoint)
+ * so the client can upload the image bytes directly, bypassing the server.
+ * After the PUT completes, the client must call PATCH /api/profile/avatar
+ * with the returned key to record it in PocketBase.
+ *
+ * Returns: { upload_url: string, key: string }
  */
 export const POST: RequestHandler = async ({ request, locals }) => {
 	if (!locals.user) error(401, 'Not authenticated');
 
-	const contentType = request.headers.get('content-type') ?? '';
-	if (!contentType.includes('multipart/form-data')) {
-		error(400, 'Expected multipart/form-data');
-	}
-
-	let formData: FormData;
+	let mimeType = 'image/jpeg';
 	try {
-		formData = await request.formData();
+		const body = await request.json();
+		if (body?.mime_type) mimeType = body.mime_type;
 	} catch {
-		error(400, 'Failed to parse form data');
+		// default to jpeg if body is missing/invalid
 	}
 
-	const file = formData.get('file');
-	if (!(file instanceof File)) error(400, 'Missing "file" field');
-
-	if (!ALLOWED_TYPES.includes(file.type)) {
-		error(400, `Unsupported image type: ${file.type}. Allowed: jpeg, png, webp, gif`);
+	if (!ALLOWED_TYPES.includes(mimeType)) {
+		error(400, `Unsupported image type: ${mimeType}. Allowed: jpeg, png, webp`);
 	}
 
-	if (file.size > MAX_SIZE) {
-		error(413, 'Image too large (max 5 MB)');
+	const { uploadUrl, key } = await presignAvatarUploadUrl(locals.user.id, mimeType);
+	return json({ upload_url: uploadUrl, key });
+};
+
+/**
+ * PATCH /api/profile/avatar
+ * Body: JSON { key: string }
+ *
+ * Called after the client has successfully PUT the image to MinIO via the
+ * presigned URL. Records the object key in PocketBase and returns a fresh
+ * presigned GET URL for immediate display.
+ *
+ * Returns: { avatar_url: string | null }
+ */
+export const PATCH: RequestHandler = async ({ request, locals }) => {
+	if (!locals.user) error(401, 'Not authenticated');
+
+	let key: string | undefined;
+	try {
+		const body = await request.json();
+		if (typeof body?.key === 'string') key = body.key;
+	} catch {
+		error(400, 'Invalid JSON body');
 	}
 
-	const buffer = new Uint8Array(await file.arrayBuffer());
-	const key = await putAvatar(locals.user.id, buffer, file.type);
+	if (!key) error(400, 'Missing "key" field');
 
-	// Persist key in PocketBase so we can look it up later
 	await updateUserAvatarUrl(locals.user.id, key);
 
-	// Return a fresh presigned URL for immediate use
 	const avatarUrl = await presignAvatarUrl(locals.user.id);
 	return json({ avatar_url: avatarUrl });
 };
 
 /**
  * GET /api/profile/avatar
- * Returns a presigned URL for the current user's avatar, or null if none set.
+ * Returns a presigned GET URL for the current user's avatar, or null if none set.
  */
 export const GET: RequestHandler = async ({ locals }) => {
 	if (!locals.user) error(401, 'Not authenticated');
 
-	// First try to get from PocketBase record (the stored key acts as a flag)
 	const record = await getUserByUsername(locals.user.username).catch(() => null);
 	if (!record?.avatar_url) {
 		return json({ avatar_url: null });