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/81e13f4b2c8942dca536bfe23e2bf1dc/_urls.json

@@ -0,0 +1,46 @@
+{
+  "detail_url": "https://oshwhub.com/jie326513988/ESP32mi-ni-mo-shui-ping-MP3shou-",
+  "cover_url": "https://image.lceda.cn/pullimage/1kkoNNRel8HGTyfXE6rdvuyIrhsZIB9yjFK1ylZ7.jpeg",
+  "attachments": [
+    {
+      "name": "Cyberpunks.ttf",
+      "url": "https://image.lceda.cn/attachments/2023/4/FaXJtSAljzxOzElvWD0rsMFXZX56SPkOcKRm4xGf.ttf",
+      "original_id": "66f1c1dd48ef4283a5a8bb8b7b50a66a"
+    },
+    {
+      "name": "物料清单立创+部分淘宝bom.xls",
+      "url": "https://image.lceda.cn/attachments/2023/7/PPPNsIXXMw50pCHsnQuNZBgIoM49vsXwf2qInDKC",
+      "original_id": "1a1c3bb2fc9a435ba873da25c1c3a5a4"
+    },
+    {
+      "name": "外壳图案资料20230706.zip",
+      "url": "https://image.lceda.cn/attachments/2023/7/wGGJGWzVPQFAImdmJd31DCIyjENbCEb7vjiIYYQV.zip",
+      "original_id": "8f1eb2fdc3e54d538b3cb32559b8cd3b"
+    },
+    {
+      "name": "表盘.zip",
+      "url": "https://image.lceda.cn/attachments/2023/7/m6DKCeJZpyoUsMStcSZVrQWq0v3Zgi5NEdiKqWe8.zip",
+      "original_id": "0e80d3858bbe4f959d5ef3956c48fba1"
+    },
+    {
+      "name": "面板版本外壳-esp32墨水屏MP3-20230919.zip",
+      "url": "https://image.lceda.cn/attachments/2023/9/Q81VwGBXWiLedMBnxJBDNtfbmmq85YeOPWYgDePY.zip",
+      "original_id": "bfcdb0f390d94341b1ecd2250c10c804"
+    },
+    {
+      "name": "普通版本外壳-esp32墨水屏MP3-20230919.zip",
+      "url": "https://image.lceda.cn/attachments/2023/9/VroBZkfv7LXvIp3HqkR3pq1Je3y4oLBWs4ronIo0.zip",
+      "original_id": "46448bf25dd9417ab53d6ced586d8baa"
+    },
+    {
+      "name": "表盘制作工具0.2.zip",
+      "url": "https://image.lceda.cn/attachments/2023/9/ANLnOyLWWbrKDtVSXVUbXmIlwVnGbPJibmEEl4Mi.zip",
+      "original_id": "b4459dd540c44c37b74f1a2b2cae80e7"
+    },
+    {
+      "name": "UID加密算法.zip",
+      "url": "https://image.lceda.cn/attachments/2023/10/5oCvFHmOra8HBQi7tRzHrALoECQCaz6684kXrsrG.zip",
+      "original_id": "dcf13b4c76d9462bbdb37f33f781eff9"
+    }
+  ]
+}