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/766b89cd189e4f6eb068ec10a97a85d9/metadata.json

@@ -0,0 +1,40 @@
+{
+  "source": "oshwhub",
+  "source_url": "https://oshwhub.com/zjsxzc217/simplefoc_-tai-gong-shuai-shuang-tong-dao",
+  "project_id": "766b89cd189e4f6eb068ec10a97a85d9",
+  "title": "SIMPLEFOC_无刷电机大功率双通道驱动（已验证）",
+  "description_short": "应该是市面上最便宜的方案吧\n双路大功率无刷直流电机驱动\n支持arduino,esp32,esp8266,stm32等~\n支持simplefoc",
+  "description_path": "description.md",
+  "author": {
+    "username": "zjsxzc217",
+    "display_name": "成真科技",
+    "user_id": "069b70d2bd1c419693106844aa9a89c3"
+  },
+  "license": "GPL 3.0",
+  "tags": [],
+  "created_at": "2021-12-11T12:42:08.000Z",
+  "updated_at": "2026-01-20T04:26:51.000Z",
+  "published_at": "2022-07-28T12:48:19.000Z",
+  "crawled_at": "2026-04-28T17:28:39.321583+00:00",
+  "metrics": {
+    "likes": 374,
+    "stars": 875,
+    "forks": 559,
+    "views": 95275,
+    "watch": 0,
+    "comments": 118
+  },
+  "cover": {
+    "url": "https://image.lceda.cn/pullimage/vIJaZGaQy2Mr6oSwTRgwMY3u9587uXIUrnOItBgi.jpeg",
+    "path": null
+  },
+  "files": [],
+  "raw_fields": {
+    "path": "zjsxzc217/simplefoc_-tai-gong-shuai-shuang-tong-dao",
+    "grade": 4,
+    "origin": "std",
+    "public": true,
+    "publish": true,
+    "skipped_files": []
+  }
+}