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/6f0c151b366d46fe90126093dd604afe/metadata.json

@@ -0,0 +1,68 @@
+{
+  "source": "oshwhub",
+  "source_url": "https://oshwhub.com/ran-pang/multifunctional-keyboard",
+  "project_id": "6f0c151b366d46fe90126093dd604afe",
+  "title": "承载我所有幻想的键盘",
+  "description_short": "支持WIFI的4模机械键盘（USB、蓝牙、WIFI、2.4G接收器），搭载可拆卸FOC旋钮屏，支持SurfaceDial，支持多功能磁吸扩展（例如小键盘等），支持语音交互。",
+  "description_path": "description.md",
+  "author": {
+    "username": "ran-pang",
+    "display_name": "蓝星多面体",
+    "user_id": "67341ef1bd084fdc82253c172303c478"
+  },
+  "license": "CC BY-NC-SA 3.0",
+  "tags": [],
+  "created_at": "2024-04-09T03:31:50.000Z",
+  "updated_at": "2026-03-02T03:04:18.131Z",
+  "published_at": "2026-03-02T03:05:48.000Z",
+  "crawled_at": "2026-04-28T17:00:27.915251+00:00",
+  "metrics": {
+    "likes": 844,
+    "stars": 1702,
+    "forks": 0,
+    "views": 140596,
+    "watch": 0,
+    "comments": 168
+  },
+  "cover": {
+    "url": "https://image.lceda.cn/oshwhub/bc1b869340da45b5b133f7873ef0316b.png",
+    "path": "cover.png"
+  },
+  "files": [
+    {
+      "name": "3D文件20240817.rar",
+      "url": "https://image.lceda.cn/oshwhub/project/attachments/dcf4d546b4894095856ff26602311d74.rar",
+      "original_id": "c77a544f30db4e9995b1fb9d98191a1f",
+      "ext": "rar",
+      "mime": "application/octet-stream",
+      "size": 1897642,
+      "md5": "7992584193ce365e8dc5802ba6378d3d"
+    },
+    {
+      "name": "结构&电子料BOM20241015.xlsx",
+      "url": "https://image.lceda.cn/oshwhub/project/attachments/c8e7f1b55c804bb1b02978aa2e041a32.xlsx",
+      "original_id": "a1e0506d93ec450eaa9836aa2d772116",
+      "ext": "xlsx",
+      "mime": "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet",
+      "size": 545926,
+      "md5": "ac573dde597d488d5b870d08c52994ec"
+    },
+    {
+      "name": "软件包.txt",
+      "url": "https://image.lceda.cn/oshwhub/project/attachments/3cdec58f4ae242cc9c967dc3560cef65.txt",
+      "original_id": "569011b22e7448b3ada12eb65391b1f7",
+      "ext": "txt",
+      "mime": "text/plain",
+      "size": 84,
+      "md5": "f62b54529f79a84682e082e7ad79035c"
+    }
+  ],
+  "raw_fields": {
+    "path": "ran-pang/multifunctional-keyboard",
+    "grade": 4,
+    "origin": "pro",
+    "public": true,
+    "publish": true,
+    "skipped_files": []
+  }
+}