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/977b637a85fa44fbb5d4214373576a04/_urls.json

@@ -0,0 +1,21 @@
+{
+  "detail_url": "https://oshwhub.com/littleoandlittleq/bian-xie-jia-re-tai",
+  "cover_url": "https://image.lceda.cn/pullimage/jDqTDFPFZtipYNYB0YLY3eLCALiFStAnJA1XThW3.jpeg",
+  "attachments": [
+    {
+      "name": "mini加热台.zip",
+      "url": "https://image.lceda.cn/attachments/2022/9/OkmFIAc4W0oNO8id981Qx2HKDQGtHhELtrRruSez.zip",
+      "original_id": "66b490db01644182832744519a3eff2d"
+    },
+    {
+      "name": "演示.mp4",
+      "url": "https://image.lceda.cn/attachments/2022/9/fLXJRIwKZjyC3D5FmiSZGuped1OWzDJwemEu5ol1.mp4",
+      "original_id": "30778162d135432b9cf7930da02767cc"
+    },
+    {
+      "name": "HeatingPlate-PD-修复温度频繁跳变.hex",
+      "url": "https://image.lceda.cn/attachments/2022/10/Vh04GZajs1OSanjeymaWCZmpykJZAZmaf52kIlqG.txt",
+      "original_id": "4e4451d2c57e4669a48152d865bdd44e"
+    }
+  ]
+}

data/raw/oshwhub/977b637a85fa44fbb5d4214373576a04/description.md

@@ -0,0 +1,9 @@
+# [PD协议 | 高颜值]mini加热台
+
+超迷你的加热台，PD20V供电，加热面大小5.6*5.6cm，可以通过两个按键设置参数。
+
+---
+- Source: https://oshwhub.com/littleoandlittleq/bian-xie-jia-re-tai
+- Author: 小O和小Q (littleoandlittleq)
+- License: GPL 3.0
+- Published: 2023-07-27T01:58:31.000Z

data/raw/oshwhub/977b637a85fa44fbb5d4214373576a04/metadata.json

@@ -0,0 +1,68 @@
+{
+  "source": "oshwhub",
+  "source_url": "https://oshwhub.com/littleoandlittleq/bian-xie-jia-re-tai",
+  "project_id": "977b637a85fa44fbb5d4214373576a04",
+  "title": "[PD协议 | 高颜值]mini加热台",
+  "description_short": "超迷你的加热台，PD20V供电，加热面大小5.6*5.6cm，可以通过两个按键设置参数。",
+  "description_path": "description.md",
+  "author": {
+    "username": "littleoandlittleq",
+    "display_name": "小O和小Q",
+    "user_id": "9ff80e24b505422a87c592cd4c6efb69"
+  },
+  "license": "GPL 3.0",
+  "tags": [],
+  "created_at": "2022-09-12T11:49:10.000Z",
+  "updated_at": "2026-04-03T01:41:10.000Z",
+  "published_at": "2023-07-27T01:58:31.000Z",
+  "crawled_at": "2026-04-28T16:59:36.937187+00:00",
+  "metrics": {
+    "likes": 994,
+    "stars": 2257,
+    "forks": 0,
+    "views": 218248,
+    "watch": 0,
+    "comments": 728
+  },
+  "cover": {
+    "url": "https://image.lceda.cn/pullimage/jDqTDFPFZtipYNYB0YLY3eLCALiFStAnJA1XThW3.jpeg",
+    "path": "cover.jpeg"
+  },
+  "files": [
+    {
+      "name": "mini加热台.zip",
+      "url": "https://image.lceda.cn/attachments/2022/9/OkmFIAc4W0oNO8id981Qx2HKDQGtHhELtrRruSez.zip",
+      "original_id": "66b490db01644182832744519a3eff2d",
+      "ext": "zip",
+      "mime": "application/x-zip-compressed",
+      "size": 1016755,
+      "md5": "09024a961bdccf4fbfd869fb372ef398"
+    },
+    {
+      "name": "演示.mp4",
+      "url": "https://image.lceda.cn/attachments/2022/9/fLXJRIwKZjyC3D5FmiSZGuped1OWzDJwemEu5ol1.mp4",
+      "original_id": "30778162d135432b9cf7930da02767cc",
+      "ext": "mp4",
+      "mime": "video/mp4",
+      "size": 12091219,
+      "md5": "b79ba5183adaf449c33fea9e52245b1e"
+    },
+    {
+      "name": "HeatingPlate-PD-修复温度频繁跳变.hex",
+      "url": "https://image.lceda.cn/attachments/2022/10/Vh04GZajs1OSanjeymaWCZmpykJZAZmaf52kIlqG.txt",
+      "original_id": "4e4451d2c57e4669a48152d865bdd44e",
+      "ext": "txt",
+      "mime": "application/octet-stream",
+      "size": 90235,
+      "md5": "1eafa1f681c8d988c1213b28de8fe2e3"
+    }
+  ],
+  "raw_fields": {
+    "path": "littleoandlittleq/bian-xie-jia-re-tai",
+    "grade": 4,
+    "origin": "pro",
+    "public": true,
+    "publish": true,
+    "skipped_files": []
+  }
+}