crawler: --no-cover, --concurrency, drop cross-host sleep + batch-50 Step 1 done

Three crawler ergonomics for batch operations:

--no-cover  Skip cover image download. For scan-only modes (license/meta
            scrape) this drops ~1.3s/project and avoids slow-CDN hangs.

--concurrency N  ThreadPoolExecutor wrapping the per-project loop. Default
                 1 = serial (current behavior). Anonymous endpoints tolerate
                 5+ comfortably; output uses a print lock for readable
                 interleaved progress. fetch_cover plumbs through crawl_one.

Drop cross-host sleep #1: in crawl_one between detail HTML (oshwhub.com)
and cover image (image.lceda.cn). Different hosts — sleep was unnecessary.
Saves ~1s/project. Sleep #2 (post-cover, before next iteration) stays — it
gates the next oshwhub.com hit.

download_to gains max_seconds wall budget (default 60s, cover uses 15s).
Defends against pathologically slow CDN connections — observed 10 KB/s
on image.lceda.cn for one project, would have hung 6+ min on a 3.6 MB
cover otherwise. httpx default timeout resets per chunk, so streaming
downloads need an external wall-clock guard.

batch-50 Step 1 (license/meta scrape) shipped:
  50/50 candidates have metadata.json + license recorded
  License distribution: GPL 3.0 32, Public Domain 6, NC variants 8,
                        CERN-OHL 1, MIT 1, CC BY 3.0 1
  Forge-friendly (non-NC): 41/50 (82%)
  Declared attachments: 180 files / 2.36 GB (median 18 MB/proj, max 304 MB)
  Walltime: 3min 26s for 28 projects at concurrency=5 (server-side
            HTML render bound, not sleep-bound)

One orphan partial cover (a670e60a...) cleaned up — leftover from the
first aborted run before the timeout fix landed.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

data/raw/oshwhub/c610a9bc18ac4a17a88ab6e427a25d6f/metadata.json

@@ -0,0 +1,86 @@
+{
+  "source": "oshwhub",
+  "source_url": "https://oshwhub.com/buerchen/t12-han-bi-v6-1",
+  "project_id": "c610a9bc18ac4a17a88ab6e427a25d6f",
+  "title": "T12焊笔v6.1",
+  "description_short": "新版T12焊笔替换0.5寸OLED 88*48 CH1115驱动 IIC ，兼容ESP8266和ESP8285，新增3D打印外壳。",
+  "description_path": "description.md",
+  "author": {
+    "username": "buerchen",
+    "display_name": "_buerchen",
+    "user_id": "110e585640d34b5fb6cf40cad05cf172"
+  },
+  "license": "GPL 3.0",
+  "tags": [],
+  "created_at": "2022-05-02T11:59:59.000Z",
+  "updated_at": "2026-03-16T03:41:16.000Z",
+  "published_at": "2023-07-03T08:02:40.000Z",
+  "crawled_at": "2026-04-28T17:24:10.971402+00:00",
+  "metrics": {
+    "likes": 570,
+    "stars": 1049,
+    "forks": 0,
+    "views": 81684,
+    "watch": 0,
+    "comments": 485
+  },
+  "cover": {
+    "url": "https://image.lceda.cn/pullimage/ISDYxW65ecUhy445f7Zox1TZqXdNaLGWWTKuZMfG.jpeg",
+    "path": "cover.jpeg"
+  },
+  "files": [
+    {
+      "name": "T12焊笔6.1程序相关.zip",
+      "url": "https://image.lceda.cn/attachments/2022/5/bDSs3rg65zxeXtYIAQqLgB3eppFXKi0YJHcPwXEL.zip",
+      "original_id": "94d622c31a724b5683cfd52e60ed4d9f",
+      "ext": "zip",
+      "mime": "application/x-zip-compressed",
+      "size": 46210407,
+      "md5": "6f172b0899a7cefc6efd95ace4dc535c"
+    },
+    {
+      "name": "BOM_T12焊笔v6.1.xlsx",
+      "url": "https://image.lceda.cn/attachments/2022/5/dJ927VmhzY96eAwIwUPQrUajvyIRAVp3VFKtc4yW.xlsx",
+      "original_id": "7f996b1da5eb4fa08ba7fdb008e3cb69",
+      "ext": "xlsx",
+      "mime": "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet",
+      "size": 11601,
+      "md5": "68ed3500c258809ae16aa76e29592e3b"
+    },
+    {
+      "name": "T12焊笔v6.1模型文件.rar",
+      "url": "https://image.lceda.cn/attachments/2022/5/BOJzMOjfkn0ZiijBO4tUH2A3ZqNo4SkIn1gWSZHh.rar",
+      "original_id": "475e14d57df540a09138785f0992386c",
+      "ext": "rar",
+      "mime": "application/octet-stream",
+      "size": 2211113,
+      "md5": "a834ecd2bca7d704e57f3c44b0a40fc3"
+    },
+    {
+      "name": "打印外壳触摸验证.mp4",
+      "url": "https://image.lceda.cn/attachments/2022/5/huIg1aaPwhDhnOC11uRtmzK5nzQTfjuf2ktBmHMs.mp4",
+      "original_id": "eca04fd4644f4bfc9a4a1963c8972126",
+      "ext": "mp4",
+      "mime": "video/mp4",
+      "size": 18044374,
+      "md5": "cf27f504cbefefc0b887b2767e3bfcad"
+    },
+    {
+      "name": "Gerber_PCB_T12焊笔v6.1.zip",
+      "url": "https://image.lceda.cn/attachments/2022/5/FpHLoahmhudObo5jNnNoMtyjM0PG8CrniAvIMtzP.zip",
+      "original_id": "65421fe005c94e89a8456384c7db813b",
+      "ext": "zip",
+      "mime": "application/x-zip-compressed",
+      "size": 276875,
+      "md5": "e65a79eaef6fa3aaad7d40ce560ddd3d"
+    }
+  ],
+  "raw_fields": {
+    "path": "buerchen/t12-han-bi-v6-1",
+    "grade": 4,
+    "origin": "pro",
+    "public": true,
+    "publish": true,
+    "skipped_files": []
+  }
+}