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/72312817efb6449ca520216c820c432c/metadata.json

@@ -0,0 +1,77 @@
+{
+  "source": "oshwhub",
+  "source_url": "https://oshwhub.com/logicworld/h6_board",
+  "project_id": "72312817efb6449ca520216c820c432c",
+  "title": "全志H6开发板-从零入门ARM高速电路设计",
+  "description_short": "本项目开源主要目的是帮助想学ARM高速电路的小伙伴们，学会自己做一个ARM开发板(eg. 全志H6开发板)。快来看看是否真从零入门，有手就行！",
+  "description_path": "description.md",
+  "author": {
+    "username": "logicworld",
+    "display_name": "logicworld",
+    "user_id": "0d18a61fce2a475c94847e0ea05339a5"
+  },
+  "license": "CERN Open Hardware License",
+  "tags": [],
+  "created_at": "2022-11-06T14:43:51.000Z",
+  "updated_at": "2026-04-15T05:12:30.000Z",
+  "published_at": "2023-12-11T05:43:19.000Z",
+  "crawled_at": "2026-04-28T17:14:05.134789+00:00",
+  "metrics": {
+    "likes": 694,
+    "stars": 1459,
+    "forks": 0,
+    "views": 146963,
+    "watch": 0,
+    "comments": 166
+  },
+  "cover": {
+    "url": "https://image.lceda.cn/pullimage/UZTlVGjHIwdTBM7U8a8MdYdS6STOC7WwmBpuVb6J.jpeg",
+    "path": "cover.jpeg"
+  },
+  "files": [
+    {
+      "name": "DragonHDV1.7.7.rar",
+      "url": "https://image.lceda.cn/attachments/2023/2/SIV1i7lcm2Kv2p0Pk5JsruEk0YuNW6WsJLdlQTu2.rar",
+      "original_id": "298483d9407c4f50923fab5a1ca3b30d",
+      "ext": "rar",
+      "mime": "application/octet-stream",
+      "size": 5167713,
+      "md5": "3f296d4b3a0e3a9176a8153dc33f4217"
+    },
+    {
+      "name": "PhoenixInstall.zip",
+      "url": "https://image.lceda.cn/attachments/2023/2/yJyXOAeuuNuj5hpE0eTlgmZ7VlksTQiEzD6rNcXA.zip",
+      "original_id": "6ce9943e6a014c4a90c5e3303830c3f6",
+      "ext": "zip",
+      "mime": "application/x-zip-compressed",
+      "size": 15659965,
+      "md5": "0d5507521921660e8b90acfba7751d5a"
+    },
+    {
+      "name": "VID_20230226_005335_音乐播放.mp4",
+      "url": "https://image.lceda.cn/attachments/2023/2/nPqrMOKDAMpaaCTNdKB60VeWpyd9Rg4EIB0kepQZ.mp4",
+      "original_id": "a2507f7d8e7e4f209d9988443f7a49a3",
+      "ext": "mp4",
+      "mime": "video/mp4",
+      "size": 43169321,
+      "md5": "b709ef3340ce7b381215a55e2f2aa4f7"
+    },
+    {
+      "name": "VID_20230226_032216_3D测试.mp4",
+      "url": "https://image.lceda.cn/attachments/2023/2/RkVfx9191D4eTxvKW9Hb3LeNSFS3tttHBR2r49OT.mp4",
+      "original_id": "8e10973248664574b87d95d0f3d82d9f",
+      "ext": "mp4",
+      "mime": "video/mp4",
+      "size": 49166774,
+      "md5": "9e9e35ad8f2a0ac26e84b2b8d4e9d1dd"
+    }
+  ],
+  "raw_fields": {
+    "path": "logicworld/h6_board",
+    "grade": 4,
+    "origin": "pro",
+    "public": true,
+    "publish": true,
+    "skipped_files": []
+  }
+}