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/d865cb8992f1437ca728ed11b9ec9421/metadata.json

@@ -0,0 +1,50 @@
+{
+  "source": "oshwhub",
+  "source_url": "https://oshwhub.com/sngelswyh/stm32-smart-desktop-pet",
+  "project_id": "d865cb8992f1437ca728ed11b9ec9421",
+  "title": "STM32智能桌面宠物",
+  "description_short": "可以进行一些简单的交流互动，立正，前进，后退，左转，右转，摇尾巴，趴下，蹲下，睡觉，向前跳，打招呼，伸懒腰等，一般用于放置桌面上。语音可以自定义设置，需要到智能公元网站自行配置。",
+  "description_path": "description.md",
+  "author": {
+    "username": "sngelswyh",
+    "display_name": "Sngels_wyh",
+    "user_id": "f5e5983cd8e94ba3b7f01b6e21d709b8"
+  },
+  "license": "GPL 3.0",
+  "tags": [],
+  "created_at": "2024-12-15T08:48:43.151Z",
+  "updated_at": "2026-03-29T11:08:51.451Z",
+  "published_at": "2026-03-30T03:13:02.395Z",
+  "crawled_at": "2026-04-28T16:59:30.460189+00:00",
+  "metrics": {
+    "likes": 1525,
+    "stars": 2766,
+    "forks": 0,
+    "views": 362182,
+    "watch": 0,
+    "comments": 698
+  },
+  "cover": {
+    "url": "https://image.lceda.cn/oshwhub/pullImage/35077647fee7471cb3f2dacc50ec3b37.jpg",
+    "path": "cover.jpg"
+  },
+  "files": [
+    {
+      "name": "注意：资料链接整理到了描述的最后（实物图的后面）.txt",
+      "url": "https://image.lceda.cn/oshwhub/project/attachments/7603392e0fd54c5890f3f86de7658bd2.txt",
+      "original_id": "c2e01aa1724742cc8540ff3c07109a6a",
+      "ext": "txt",
+      "mime": "text/plain",
+      "size": 0,
+      "md5": "d41d8cd98f00b204e9800998ecf8427e"
+    }
+  ],
+  "raw_fields": {
+    "path": "sngelswyh/stm32-smart-desktop-pet",
+    "grade": 3,
+    "origin": "pro",
+    "public": true,
+    "publish": true,
+    "skipped_files": []
+  }
+}