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/7e052d660aeb40aa9d47a558dd26175b/_urls.json

@@ -0,0 +1,51 @@
+{
+  "detail_url": "https://oshwhub.com/MisakaBanBan/small_desktop_display",
+  "cover_url": "https://image.lceda.cn/pullimage/0LC1VDEuA4FbpmzIHiFUESChNyIlnzC53NkgSSYf.jpeg",
+  "attachments": [
+    {
+      "name": "主体1.1.STL",
+      "url": "https://image.lceda.cn/attachments/2021/11/xOrezqcPbYfK9VnhQkYi124QpVqh6xPs7Htet9Ya.bin",
+      "original_id": "244c72ea5fcd4948bdec53d2c12eabd4"
+    },
+    {
+      "name": "后壳1.1.STL",
+      "url": "https://image.lceda.cn/attachments/2021/11/WW1CzjTYoa5HusYGS8TxqACFOGE55DoUA1EgLWhV.bin",
+      "original_id": "6ffa112d22f3418fa51ff6fa85fbdde1"
+    },
+    {
+      "name": "必读.txt",
+      "url": "https://image.lceda.cn/attachments/2021/11/Sj2hze8FxYUKfdhwcp0xB0xyfAMzhhVOJoIZaoh5.txt",
+      "original_id": "98fe382e770f49a98f88999bc59fca1e"
+    },
+    {
+      "name": "主体1.2.STL",
+      "url": "https://image.lceda.cn/attachments/2021/11/injkPVhnFMdBvV1LlacSNaAlKz3XBgUwtS1Zl2lx.bin",
+      "original_id": "5c5a5806f96f454b9647646f6a8e355c"
+    },
+    {
+      "name": "后壳1.2.STL",
+      "url": "https://image.lceda.cn/attachments/2021/11/foqqHcSvBQ8OjvrJRCBNwvGdI1fZboKJ3tfmFUhI.bin",
+      "original_id": "daf6ccc6850648d38f4dd33b49c7be50"
+    },
+    {
+      "name": "SD²固件V1.2.zip",
+      "url": "https://image.lceda.cn/attachments/2021/11/UKGFg66qwUPWm8xD3FsHv1bHuvJDOqnm9NxD4ilG.zip",
+      "original_id": "c1c474f792b745ef829dfcb6fb28284f"
+    },
+    {
+      "name": "SD²固件V1.3.4（WEB配网+wifi休眠）by 微车游.zip",
+      "url": "https://image.lceda.cn/attachments/2021/11/cSE9vRQNPZwGVBLIPpBfsIexEgGXvLHLN6LuHHig.zip",
+      "original_id": "f241ab192d554b54909d73570706a062"
+    },
+    {
+      "name": "SD²固件操作说明V1.2.pdf",
+      "url": "https://image.lceda.cn/attachments/2021/11/oecH8BquK7sEKVzrpCmLq6Omu0y8iBsGunZEGEZz.pdf",
+      "original_id": "b34e609a934949f6bc1eafd1dc6b0b12"
+    },
+    {
+      "name": "小白专用傻瓜式更新固件教程.pdf",
+      "url": "https://image.lceda.cn/attachments/2021/11/A2NfAqKhGFWuZnFPPQbLob6rXfPrYH9FjWGrWONa.pdf",
+      "original_id": "986d97e7bd954d51a77a2aca7ce94cb7"
+    }
+  ]
+}