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/8101a18ad83a49b8937b4c3b25d4490a/metadata.json

@@ -0,0 +1,104 @@
+{
+  "source": "oshwhub",
+  "source_url": "https://oshwhub.com/course-examples/bot-dog",
+  "project_id": "8101a18ad83a49b8937b4c3b25d4490a",
+  "title": "EDA-Robot机器狗",
+  "description_short": "此项目采用ESP8266主控，支持手机遥控，采用插件封装，非常适合新手焊接。",
+  "description_path": "description.md",
+  "author": {
+    "username": "course-examples",
+    "display_name": "EDA课程案例团队",
+    "user_id": "ebbda44292b4423b92db6e999d50f4d4"
+  },
+  "license": "GPL 3.0",
+  "tags": [],
+  "created_at": "2024-11-29T03:28:45.000Z",
+  "updated_at": "2025-12-13T09:17:08.000Z",
+  "published_at": "2025-11-19T01:45:41.000Z",
+  "crawled_at": "2026-04-28T17:00:57.645264+00:00",
+  "metrics": {
+    "likes": 470,
+    "stars": 1259,
+    "forks": 0,
+    "views": 152521,
+    "watch": 0,
+    "comments": 754
+  },
+  "cover": {
+    "url": "https://image.lceda.cn/oshwhub/b5a3370cb7994efc8d4051635879d0a1.jpg",
+    "path": "cover.jpg"
+  },
+  "files": [
+    {
+      "name": "EDA-Robot演示视频.mp4",
+      "url": "https://image.lceda.cn/oshwhub/project/attachments/b3f76c6e5f174920be5ff881c51cb053.mp4",
+      "original_id": "94da385b92e5447aaa4a8b5aa2921136",
+      "ext": "mp4",
+      "mime": "video/mp4",
+      "size": 24759450,
+      "md5": "160406f1413498f31416cf842c713994"
+    },
+    {
+      "name": "EDA-Robot机器狗项目.zip",
+      "url": "https://image.lceda.cn/oshwhub/project/attachments/79ea8924fab54c65a5060b3d5df74900.zip",
+      "original_id": "c7187eb4deb046398d8f9a47020da3c1",
+      "ext": "zip",
+      "mime": "application/x-zip-compressed",
+      "size": 12758243,
+      "md5": "83de9d97c0e3870aa760677594a0d17b"
+    },
+    {
+      "name": "EDA-Robot(180度舵机版)_V1.0.zip",
+      "url": "https://image.lceda.cn/oshwhub/project/attachments/2686655fc5e54288b6389d81cb3d9545.zip",
+      "original_id": "77008a152d1142c7b8bada57efba4f16",
+      "ext": "zip",
+      "mime": "application/x-zip-compressed",
+      "size": 35138116,
+      "md5": "14f2cbf414e4f6bcbb3a5a29f5abbf70"
+    },
+    {
+      "name": "EDA-Robot(180度舵机版)_V1.1.zip",
+      "url": "https://image.lceda.cn/oshwhub/project/attachments/1cbae5b1f7ed4f9d9209d771c856396a.zip",
+      "original_id": "9b5ab50965a946eab2f7326ade3b7465",
+      "ext": "zip",
+      "mime": "application/x-zip-compressed",
+      "size": 33947718,
+      "md5": "3d5586dd37668fe4e162ffb09fab569f"
+    },
+    {
+      "name": "软件源码.zip",
+      "url": "https://image.lceda.cn/oshwhub/project/attachments/3d5e14de313647bcbc6fd047787b4c71.zip",
+      "original_id": "1a79d93c790847a39aca291ce940a60e",
+      "ext": "zip",
+      "mime": "application/x-zip-compressed",
+      "size": 133471671,
+      "md5": "7a0329bee3818a0f3cf9a1686306d259"
+    },
+    {
+      "name": "EDA-Robot(360度舵机版).zip",
+      "url": "https://image.lceda.cn/oshwhub/project/attachments/1f105ddb15984777b02b3d6a41b089f5.zip",
+      "original_id": "8996994d4a1646b888a230163fba5534",
+      "ext": "zip",
+      "mime": "application/x-zip-compressed",
+      "size": 33958851,
+      "md5": "b3d9b55a945d912200b12c688179c497"
+    },
+    {
+      "name": "简易四足机器狗物料清单.xlsx",
+      "url": "https://image.lceda.cn/oshwhub/project/attachments/a4df9115d8274e9d8caf18fcf3efd458.xlsx",
+      "original_id": "dd7f90c81c5143d48b48897b99bd41ea",
+      "ext": "xlsx",
+      "mime": "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet",
+      "size": 13656,
+      "md5": "986b4807999106200cdceb2ad6f5f426"
+    }
+  ],
+  "raw_fields": {
+    "path": "course-examples/bot-dog",
+    "grade": 4,
+    "origin": "pro",
+    "public": true,
+    "publish": true,
+    "skipped_files": []
+  }
+}