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/29ff00b5fc83498681271320e8855bc7/_urls.json

@@ -0,0 +1,5 @@
+{
+  "detail_url": "https://oshwhub.com/OSHWHubkai-yuan-ying-jian/li-chuangeda-chi-zi",
+  "cover_url": "https://image.lceda.cn/avatars/2019/10/hHC7BjrPKr531ZhNUxlskERviQATlXmSTbjH2IM8.jpeg",
+  "attachments": []
+}

data/raw/oshwhub/29ff00b5fc83498681271320e8855bc7/description.md

@@ -0,0 +1,9 @@
+# 立创EDA尺子（PCB直尺）
+
+立创EDA官方使用立创EDA设计的PCB尺子，喜欢可以直接在嘉立创下单生产
+
+---
+- Source: https://oshwhub.com/OSHWHubkai-yuan-ying-jian/li-chuangeda-chi-zi
+- Author: OSHWHub开源硬件 (OSHWHubkai-yuan-ying-jian)
+- License: GPL 3.0
+- Published: 2023-03-22T09:43:20.000Z

data/raw/oshwhub/29ff00b5fc83498681271320e8855bc7/metadata.json

@@ -0,0 +1,45 @@
+{
+  "source": "oshwhub",
+  "source_url": "https://oshwhub.com/OSHWHubkai-yuan-ying-jian/li-chuangeda-chi-zi",
+  "project_id": "29ff00b5fc83498681271320e8855bc7",
+  "title": "立创EDA尺子（PCB直尺）",
+  "description_short": "立创EDA官方使用立创EDA设计的PCB尺子，喜欢可以直接在嘉立创下单生产",
+  "description_path": "description.md",
+  "author": {
+    "username": "OSHWHubkai-yuan-ying-jian",
+    "display_name": "OSHWHub开源硬件",
+    "user_id": "b891f6552c9941cf8931dfaefd81fca1"
+  },
+  "license": "GPL 3.0",
+  "tags": [
+    "立创EDA",
+    "OSHWHub",
+    "开源硬件",
+    "PCB尺子"
+  ],
+  "created_at": "2019-10-28T08:21:21.000Z",
+  "updated_at": "2026-03-03T01:53:42.000Z",
+  "published_at": "2023-03-22T09:43:20.000Z",
+  "crawled_at": "2026-04-28T17:27:38.530647+00:00",
+  "metrics": {
+    "likes": 663,
+    "stars": 1233,
+    "forks": 1550,
+    "views": 157579,
+    "watch": 0,
+    "comments": 99
+  },
+  "cover": {
+    "url": "https://image.lceda.cn/avatars/2019/10/hHC7BjrPKr531ZhNUxlskERviQATlXmSTbjH2IM8.jpeg",
+    "path": null
+  },
+  "files": [],
+  "raw_fields": {
+    "path": "OSHWHubkai-yuan-ying-jian/li-chuangeda-chi-zi",
+    "grade": 3,
+    "origin": "std",
+    "public": true,
+    "publish": true,
+    "skipped_files": []
+  }
+}