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/ec8a8499750b4e729d3e93e842edc68b/metadata.json

@@ -0,0 +1,77 @@
+{
+  "source": "oshwhub",
+  "source_url": "https://oshwhub.com/LiiGuang/pn532-bigant_copy_copy",
+  "project_id": "ec8a8499750b4e729d3e93e842edc68b",
+  "title": "PN532读写卡器（支持NFC、RFID）",
+  "description_short": "一个基于PN532的RFID读写器，可以读写M1、UID、CUID、FUID、带NFC功能的手环、手机等，门禁卡解决方案的不二之选。",
+  "description_path": "description.md",
+  "author": {
+    "username": "LiiGuang",
+    "display_name": "LiiGuang",
+    "user_id": "a029aa7cae0046668ef932291a5ca84a"
+  },
+  "license": "Public Domain",
+  "tags": [],
+  "created_at": "2021-12-02T09:43:03.000Z",
+  "updated_at": "2026-04-18T13:43:32.000Z",
+  "published_at": "2022-07-29T00:47:05.000Z",
+  "crawled_at": "2026-04-28T17:27:41.082884+00:00",
+  "metrics": {
+    "likes": 518,
+    "stars": 1157,
+    "forks": 611,
+    "views": 86716,
+    "watch": 0,
+    "comments": 614
+  },
+  "cover": {
+    "url": "https://image.lceda.cn/avatars/2022/7/lUdCAf1YwebqL2vP0R0y43NVBFXg8gGhnImrZg1e.png",
+    "path": null
+  },
+  "files": [
+    {
+      "name": "M1T-v1.7.0.zip",
+      "url": "https://image.lceda.cn/attachments/2022/2/5iVsqeGtrrqgcDv960bd68kq9d34tg9zkRY17kaN.zip",
+      "original_id": "b5f2234710344f6f9211ea64d7b8d78d",
+      "ext": "zip",
+      "mime": "application/x-zip-compressed",
+      "size": 3862429,
+      "md5": "7f44defd81ea8b8b5442ecc73a77f1d6"
+    },
+    {
+      "name": "IMG_5934 00_00_05-00_00_17.mp4",
+      "url": "https://image.lceda.cn/attachments/2022/2/Mi1nCCKISOFnESkSekVCPA0f4DPOydBnLWKQpcnX.mp4",
+      "original_id": "8d7054457a554ba3bafaa4185b9dd611",
+      "ext": "mp4",
+      "mime": "video/mp4",
+      "size": 6217870,
+      "md5": "b81d7d0132629f3f8dd4cc741ebeeb7f"
+    },
+    {
+      "name": "一体式PN532驱动（CH340E）.zip",
+      "url": "https://image.lceda.cn/attachments/2022/2/JBhL5FA8DWmWFFO5XKLko6BfOt3mbRbWlorC3IQS.zip",
+      "original_id": "a90fa0428ca7499c8879307198f5128a",
+      "ext": "zip",
+      "mime": "application/x-zip-compressed",
+      "size": 257656,
+      "md5": "5c196c8da861c4dab06adce94ae5223c"
+    },
+    {
+      "name": "手机连接.MOV",
+      "url": "https://image.lceda.cn/attachments/2022/5/2QBSTr4H0vZD5nQD5lU5vD2z6DjU4ZFM1SkKpSNE.qt",
+      "original_id": "3eeb2b9ceb40442282512797a798f1f9",
+      "ext": "qt",
+      "mime": "video/quicktime",
+      "size": 6492644,
+      "md5": "a5e062e276e1da1acbc093785f20b3f8"
+    }
+  ],
+  "raw_fields": {
+    "path": "LiiGuang/pn532-bigant_copy_copy",
+    "grade": 4,
+    "origin": "std",
+    "public": true,
+    "publish": true,
+    "skipped_files": []
+  }
+}