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/3e3c7725251c4456ad91cd88308944ff/_urls.json

@@ -0,0 +1,46 @@
+{
+  "detail_url": "https://oshwhub.com/yangzen/xing-huo-ji-hua-zui-gai-17-4-chu-mo-ji-xie-jian-pan-pro",
+  "cover_url": "https://image.lceda.cn/pullimage/CNLYX16K1KVs8dV2DftiiriK7beCyFGqOqwhB0rZ.jpeg",
+  "attachments": [
+    {
+      "name": "改键上位机V4.zip",
+      "url": "https://image.lceda.cn/attachments/2022/11/93XSpvEPVQrkz9y57RwO9QBchpyfut1u8DFjupmf.zip",
+      "original_id": "9d8f29b9bbd747cf94e45d906026d6d7"
+    },
+    {
+      "name": "丐17+4TPRO_Ver193.hex",
+      "url": "https://image.lceda.cn/attachments/2023/1/SRsbvzcW5A4NUuXEJ2ZbmKjQGl6kvlGP7REhLnWG.txt",
+      "original_id": "e4bc223e7fc14c86827752ea604cf7cd"
+    },
+    {
+      "name": "17键RGB键盘程序Ver1.93.zip",
+      "url": "https://image.lceda.cn/attachments/2023/2/HF87gb1qc0G86j6PZhgKa8UW6JOpj8Br4hAY6aLp.zip",
+      "original_id": "0b5e2c46025b4552b9368460e024f0bf"
+    },
+    {
+      "name": "丐17+4TPRO_Ver19F.hex",
+      "url": "https://image.lceda.cn/attachments/2023/4/twznraIbGygqNvixQTnE1BFMk79wAXrbRJL2GILX.txt",
+      "original_id": "671e946695734c3293717194b3355dfb"
+    },
+    {
+      "name": "丐17+4TPRO_Ver200.hex",
+      "url": "https://image.lceda.cn/attachments/2023/8/s5bGfVrLHt11CUmiODFmvRqvcBxB2NYGO3oTHyrz.txt",
+      "original_id": "783d613a70ca45e786da04865e9018fe"
+    },
+    {
+      "name": "丐17+4TPRO_Ver201.hex",
+      "url": "https://image.lceda.cn/attachments/2023/8/mw1i3TcYfyNcu3CQ7gF93Hkh9bOvvlpqWNkBpS5w.txt",
+      "original_id": "3a0b1b97e6ee4b6184739c081866bad2"
+    },
+    {
+      "name": "丐17+4TPRO_Ver2519.hex",
+      "url": "https://image.lceda.cn/oshwhub/project/attachments/23349b7205be4d7ba3d8a4913628f495.hex",
+      "original_id": "0f17dbb237e24cd097c77c83cda096b1"
+    },
+    {
+      "name": "丐17+4TPRO_Ver2541.hex",
+      "url": "https://image.lceda.cn/oshwhub/project/attachments/0a35f2cc9cc7475abce7436804f619e6.hex",
+      "original_id": "de023c4bdea345cb97cb17141c343161"
+    }
+  ]
+}