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/d46ef2f68e334a72961d48ba0cfbcae2/_urls.json

@@ -0,0 +1,16 @@
+{
+  "detail_url": "https://oshwhub.com/leichaolin/xing-huo-ji-hua-3.5KWda-gong-shu",
+  "cover_url": "https://image.lceda.cn/pullimage/MRyi3ahztovD8GJ41WF45V4kDsBxmjORiGMJMfgG.jpeg",
+  "attachments": [
+    {
+      "name": "大功率逆变器.rar",
+      "url": "https://image.lceda.cn/attachments/2023/4/lY5ZmDHS1pPWbkz09ArxBQzrMtOkHgWkXg1E6i1S.rar",
+      "original_id": "f52a12973e38414393a6e8e5a33e4d58"
+    },
+    {
+      "name": "测试视频~1.mp4",
+      "url": "https://image.lceda.cn/attachments/2023/4/XVzBmyirf4i9RMb2jekEkfnxKLgcj37ImQFvVNxq.mp4",
+      "original_id": "4063798e3aa641d1ad36522aef485643"
+    }
+  ]
+}

data/raw/oshwhub/d46ef2f68e334a72961d48ba0cfbcae2/description.md

@@ -0,0 +1,9 @@
+# 3.5KW大功率逆变器 【星火计划】
+
+输入24-72V输出220V的3.5KW逆变器
+
+---
+- Source: https://oshwhub.com/leichaolin/xing-huo-ji-hua-3.5KWda-gong-shu
+- Author: 雷老师讲电子 (leichaolin)
+- License: CC BY-NC-SA 4.0
+- Published: 2023-08-30T05:53:35.000Z

data/raw/oshwhub/d46ef2f68e334a72961d48ba0cfbcae2/metadata.json

@@ -0,0 +1,59 @@
+{
+  "source": "oshwhub",
+  "source_url": "https://oshwhub.com/leichaolin/xing-huo-ji-hua-3.5KWda-gong-shu",
+  "project_id": "d46ef2f68e334a72961d48ba0cfbcae2",
+  "title": "3.5KW大功率逆变器 【星火计划】",
+  "description_short": "输入24-72V输出220V的3.5KW逆变器",
+  "description_path": "description.md",
+  "author": {
+    "username": "leichaolin",
+    "display_name": "雷老师讲电子",
+    "user_id": "a481b71acdb44a3f8c8a15fe621c992f"
+  },
+  "license": "CC BY-NC-SA 4.0",
+  "tags": [],
+  "created_at": "2023-02-26T06:48:02.000Z",
+  "updated_at": "2025-09-10T00:24:08.000Z",
+  "published_at": "2023-08-30T05:53:35.000Z",
+  "crawled_at": "2026-04-28T17:24:26.121076+00:00",
+  "metrics": {
+    "likes": 536,
+    "stars": 1102,
+    "forks": 0,
+    "views": 119662,
+    "watch": 0,
+    "comments": 256
+  },
+  "cover": {
+    "url": "https://image.lceda.cn/pullimage/MRyi3ahztovD8GJ41WF45V4kDsBxmjORiGMJMfgG.jpeg",
+    "path": "cover.jpeg"
+  },
+  "files": [
+    {
+      "name": "大功率逆变器.rar",
+      "url": "https://image.lceda.cn/attachments/2023/4/lY5ZmDHS1pPWbkz09ArxBQzrMtOkHgWkXg1E6i1S.rar",
+      "original_id": "f52a12973e38414393a6e8e5a33e4d58",
+      "ext": "rar",
+      "mime": "application/octet-stream",
+      "size": 37253378,
+      "md5": "1727eb8f04cd821338651f96786ce5b6"
+    },
+    {
+      "name": "测试视频~1.mp4",
+      "url": "https://image.lceda.cn/attachments/2023/4/XVzBmyirf4i9RMb2jekEkfnxKLgcj37ImQFvVNxq.mp4",
+      "original_id": "4063798e3aa641d1ad36522aef485643",
+      "ext": "mp4",
+      "mime": "video/mp4",
+      "size": 45694880,
+      "md5": "fc5d723e587f0a1a2eb7a0982dc1e125"
+    }
+  ],
+  "raw_fields": {
+    "path": "leichaolin/xing-huo-ji-hua-3.5KWda-gong-shu",
+    "grade": 4,
+    "origin": "pro",
+    "public": true,
+    "publish": true,
+    "skipped_files": []
+  }
+}