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/f81e1c7f04774545a5c3d14212072a1e/metadata.json

@@ -0,0 +1,50 @@
+{
+  "source": "oshwhub",
+  "source_url": "https://oshwhub.com/wzw666/IP5389PRO",
+  "project_id": "f81e1c7f04774545a5c3d14212072a1e",
+  "title": "重制版IP5389[100瓦双向快充移动电源]",
+  "description_short": "基于英集芯IP5389-BZ芯片设计的双向PD100瓦移动电源方案",
+  "description_path": "description.md",
+  "author": {
+    "username": "wzw666",
+    "display_name": "小煜哥哥",
+    "user_id": "67f4ab719a2a4182934deee8cc979e93"
+  },
+  "license": "CC-BY-NC-SA 3.0",
+  "tags": [],
+  "created_at": "2022-03-31T07:05:30.000Z",
+  "updated_at": "2026-04-25T12:24:08.000Z",
+  "published_at": "2022-10-12T01:19:17.000Z",
+  "crawled_at": "2026-04-28T17:28:11.862247+00:00",
+  "metrics": {
+    "likes": 355,
+    "stars": 749,
+    "forks": 476,
+    "views": 110577,
+    "watch": 0,
+    "comments": 279
+  },
+  "cover": {
+    "url": "https://image.lceda.cn/avatars/2022/4/5l2JFttpzbTZsYK4FCpOMpfNOJviSliQkmW9yfWW.png",
+    "path": null
+  },
+  "files": [
+    {
+      "name": "元器件脚位标示图PCB_IP5389_V2.7.rar",
+      "url": "https://image.lceda.cn/attachments/2022/7/dyj2Xqub7Ow9UdoSPwSFlGSgR7JKZxbYFW7oSSt3.rar",
+      "original_id": "db117aa8dbcb4fe4a510fc3c487bd4af",
+      "ext": "rar",
+      "mime": "application/octet-stream",
+      "size": 138724,
+      "md5": "df6bedb9ce0511db5ddfd6eaa4b5d13c"
+    }
+  ],
+  "raw_fields": {
+    "path": "wzw666/IP5389PRO",
+    "grade": 3,
+    "origin": "std",
+    "public": true,
+    "publish": true,
+    "skipped_files": []
+  }
+}