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/9158ea94e9654f6eb2cca93b5c2a9c32/metadata.json

@@ -0,0 +1,77 @@
+{
+  "source": "oshwhub",
+  "source_url": "https://oshwhub.com/mondraker/snow_light",
+  "project_id": "9158ea94e9654f6eb2cca93b5c2a9c32",
+  "title": "触摸无极调光雪花灯（陶瓷灯丝）（新手小白也可以做！）",
+  "description_short": "触摸无极调光，无频闪无需烧录程序，焊接简单有教程，送朋友，当挂件都可。Type-C接口，成本不算邮费五块左右。附带焊接教程与所有物料链接！配套亚克力外壳与充电底座都已开源，迭代完成放心食用。",
+  "description_path": "description.md",
+  "author": {
+    "username": "mondraker",
+    "display_name": "mondraker",
+    "user_id": "37d334fe908b4df9b508da7318220388"
+  },
+  "license": "GPL 3.0",
+  "tags": [],
+  "created_at": "2022-04-05T15:41:17.000Z",
+  "updated_at": "2026-03-11T09:15:59.000Z",
+  "published_at": "2024-12-18T05:45:21.000Z",
+  "crawled_at": "2026-04-28T17:27:36.312889+00:00",
+  "metrics": {
+    "likes": 1036,
+    "stars": 2324,
+    "forks": 4434,
+    "views": 297150,
+    "watch": 0,
+    "comments": 524
+  },
+  "cover": {
+    "url": "https://image.lceda.cn/pullimage/mwKKTEDJaNPWViwxYvr2tgWnnFKj7F5HxOervHOT.jpeg",
+    "path": null
+  },
+  "files": [
+    {
+      "name": "ibom焊接图.zip",
+      "url": "https://image.lceda.cn/attachments/2022/9/mJq7eM9QcM48iuYmLEXudUz9SI51QOajguGM50M6.zip",
+      "original_id": "e09b393441414f80a5a6b62fd7dbea95",
+      "ext": "zip",
+      "mime": "application/x-zip-compressed",
+      "size": 253171,
+      "md5": "bbbbfc2ec5c832bbddb4138cf1f0730f"
+    },
+    {
+      "name": "立创商城下单bom.xlsx",
+      "url": "https://image.lceda.cn/attachments/2022/11/jIJMPm4JJHTxzqyryOjaNtuWqgsfm8bAEPWd4ZEf.bin",
+      "original_id": "edc3eb6f6cb34df4bc84cc663ecc8df0",
+      "ext": "bin",
+      "mime": "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet",
+      "size": 9953,
+      "md5": "53a319277da38399561eabd227775173"
+    },
+    {
+      "name": "雪花灯外壳（立创面板打印）-顶.zip",
+      "url": "https://image.lceda.cn/attachments/2023/1/qtdEa5eGGUTVhEN4BomBTWNkPGm2sz4isbpPPvP2.zip",
+      "original_id": "c966347bdc4f42098ace1a9b6ea09afb",
+      "ext": "zip",
+      "mime": "application/x-zip-compressed",
+      "size": 121058,
+      "md5": "9ef182365de5226987d457082738e2ba"
+    },
+    {
+      "name": "雪花灯外壳（立创面板打印）-底.zip",
+      "url": "https://image.lceda.cn/attachments/2023/1/IIA9aLts4pZ3FuV7X8VeodBjdvRSuXpYEK4ikMFi.zip",
+      "original_id": "0c2b7848e41846f8b5523924f84f9609",
+      "ext": "zip",
+      "mime": "application/x-zip-compressed",
+      "size": 101727,
+      "md5": "618f72537fce0fca79ec7e8b6f216723"
+    }
+  ],
+  "raw_fields": {
+    "path": "mondraker/snow_light",
+    "grade": 3,
+    "origin": "std",
+    "public": true,
+    "publish": true,
+    "skipped_files": []
+  }
+}