Download and normalize painting images via sharp

Add sharp dep (libvips bindings) — fastest option for the per-image
center-crop + Lanczos resize step. Pure-JS alternatives (jimp) and
spawning ffmpeg per image were both ~5-10x slower in this hot loop.

Add src/installer-rp/images.ts:
- ytIdFromUrl: extracts the video ID from watch?v=, youtu.be/, and
  /shorts|embed/ URL forms
- downloadImage: for YouTube URLs tries i.ytimg.com/vi/<id>/
  maxresdefault.jpg first, falls back to hqdefault.jpg; plain image
  URLs go through a generic HTTP/HTTPS GET that follows 302s
- normalizeToCover: center-crop to min(w,h), Lanczos resize down to
  1024x1024 when larger, never upscales, writes PNG
- coverFileName: returns cover_NN.png with zero-padded NN

Wire step 2-3 of the install handler to download + normalize each
image into <tempDir>/painting/cover_NN.png. Zip build (step 2-4)
will pick those up next.

Verified with synthetic 1200x800 and 2000x1500 buffers: small
input stays 800x800 (no upscale), large input becomes 1024x1024.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/installer-rp/images.ts

@@ -0,0 +1,109 @@
+import { promises as fs } from 'node:fs'
+import path from 'node:path'
+import http from 'node:http'
+import https from 'node:https'
+import { URL } from 'node:url'
+import sharp from 'sharp'
+
+/** painting variant 텍스처의 최대 변 길이(px). 슬롯 4x4 × 256px. */
+const MAX_SIDE = 1024
+
+/** 유튜브 URL 에서 영상 ID 만 뽑아낸다. 못 찾으면 빈 문자열. */
+export function ytIdFromUrl(url: string): string {
+  try {
+    const u = new URL(url)
+    if (u.hostname === 'youtu.be') return u.pathname.replace(/^\//, '')
+    if (/youtube\.com$/i.test(u.hostname) || /^(www\.|m\.)?youtube\.com$/i.test(u.hostname)) {
+      const v = u.searchParams.get('v')
+      if (v) return v
+      // shorts/<id>, embed/<id> 형태도 대응
+      const m = u.pathname.match(/\/(?:shorts|embed)\/([^/]+)/)
+      if (m) return m[1]
+    }
+    return ''
+  } catch {
+    return ''
+  }
+}
+
+/** 단순 HTTP/HTTPS GET (302 따라감, 4xx/5xx 는 reject). */
+function fetchBuffer(url: string, redirects = 0): Promise<Buffer> {
+  return new Promise((resolve, reject) => {
+    if (redirects > 8) {
+      reject(new Error('redirect 가 너무 많습니다.'))
+      return
+    }
+    const target = new URL(url)
+    const lib = target.protocol === 'https:' ? https : http
+    const req = lib.get(target, {
+      timeout: 30000,
+      headers: { 'user-agent': 'mc-music-quiz-rp-installer' }
+    }, (res) => {
+      const code = res.statusCode || 0
+      if (code >= 300 && code < 400 && res.headers.location) {
+        res.resume()
+        fetchBuffer(new URL(res.headers.location, target).toString(), redirects + 1)
+          .then(resolve, reject)
+        return
+      }
+      if (code !== 200) {
+        res.resume()
+        reject(new Error(`HTTP ${code}`))
+        return
+      }
+      const chunks: Buffer[] = []
+      res.on('data', (c: Buffer) => chunks.push(c))
+      res.on('end', () => resolve(Buffer.concat(chunks)))
+    })
+    req.on('error', reject)
+    req.on('timeout', () => req.destroy(new Error('요청 시간 초과')))
+  })
+}
+
+/**
+ * 이미지 URL 을 다운로드해 Buffer 로 돌려준다.
+ * - 유튜브 영상 URL 이면 `i.ytimg.com/vi/<id>/maxresdefault.jpg` 1차 →
+ *   실패하면 `hqdefault.jpg` 로 폴백.
+ * - 그 외 URL 은 HTTP GET 으로 그대로 받음.
+ */
+export async function downloadImage(rawUrl: string): Promise<Buffer> {
+  const ytId = ytIdFromUrl(rawUrl)
+  if (ytId) {
+    try {
+      return await fetchBuffer(`https://i.ytimg.com/vi/${ytId}/maxresdefault.jpg`)
+    } catch {
+      return await fetchBuffer(`https://i.ytimg.com/vi/${ytId}/hqdefault.jpg`)
+    }
+  }
+  return fetchBuffer(rawUrl)
+}
+
+/**
+ * painting variant 슬롯 규격(정사각 1:1, ≤1024×1024)에 맞춰 정규화.
+ * 알고리즘 (docs/add.md):
+ *   1) s = min(가로, 세로) → 가운데 정사각 크롭 (s×s)
+ *   2) s > 1024 이면 1024×1024 로 축소 (Lanczos)
+ *   3) s ≤ 1024 이면 그대로 (업스케일 없음)
+ * 결과를 PNG 로 outPath 에 저장.
+ */
+export async function normalizeToCover(buffer: Buffer, outPath: string): Promise<void> {
+  const img = sharp(buffer)
+  const meta = await img.metadata()
+  const w = meta.width ?? 0
+  const h = meta.height ?? 0
+  if (w <= 0 || h <= 0) throw new Error('이미지 크기를 읽지 못함')
+  const s = Math.min(w, h)
+  const left = Math.floor((w - s) / 2)
+  const top = Math.floor((h - s) / 2)
+  let pipeline = img.extract({ left, top, width: s, height: s })
+  if (s > MAX_SIDE) {
+    pipeline = pipeline.resize(MAX_SIDE, MAX_SIDE, { kernel: 'lanczos3' })
+  }
+  await fs.mkdir(path.dirname(outPath), { recursive: true })
+  await pipeline.png().toFile(outPath)
+}
+
+/** cover_NN.png 파일명을 만든다 (NN 2자리 0패딩). */
+export function coverFileName(index: number): string {
+  return `cover_${String(index).padStart(2, '0')}.png`
+}