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/929b16138f744f498c55840a87c141be/_urls.json

@@ -0,0 +1,11 @@
+{
+  "detail_url": "https://oshwhub.com/zhushengji/er-dai-dan-ci-ka",
+  "cover_url": "https://image.lceda.cn/pullimage/cwNUVdKKMKru1Zm3GxRHOkVtJvPBbInHGOebLFTD.jpeg",
+  "attachments": [
+    {
+      "name": "二代  2.13墨水屏单词卡全部元件及参考购买链接清单.xlsx",
+      "url": "https://image.lceda.cn/attachments/2022/10/YCexnsBhuXywlDeHuoQjw3piyFvyDLroMqswTMJv.xlsx",
+      "original_id": "c93321c4d83540899ef3cae901472780"
+    }
+  ]
+}

data/raw/oshwhub/929b16138f744f498c55840a87c141be/description.md

@@ -0,0 +1,9 @@
+# 二代单词卡--萤囊
+
+二代单词卡来啦！增加了许多新特性哦！
+
+---
+- Source: https://oshwhub.com/zhushengji/er-dai-dan-ci-ka
+- Author: 夏襄居士 (zhushengji)
+- License: Public Domain
+- Published: 2023-07-03T03:23:54.000Z

data/raw/oshwhub/929b16138f744f498c55840a87c141be/metadata.json

@@ -0,0 +1,50 @@
+{
+  "source": "oshwhub",
+  "source_url": "https://oshwhub.com/zhushengji/er-dai-dan-ci-ka",
+  "project_id": "929b16138f744f498c55840a87c141be",
+  "title": "二代单词卡--萤囊",
+  "description_short": "二代单词卡来啦！增加了许多新特性哦！",
+  "description_path": "description.md",
+  "author": {
+    "username": "zhushengji",
+    "display_name": "夏襄居士",
+    "user_id": "b3c7dee82f5b4c8cb0e631c4933af8b7"
+  },
+  "license": "Public Domain",
+  "tags": [],
+  "created_at": "2022-10-10T08:54:32.000Z",
+  "updated_at": "2026-01-21T05:43:36.000Z",
+  "published_at": "2023-07-03T03:23:54.000Z",
+  "crawled_at": "2026-04-28T17:29:01.316047+00:00",
+  "metrics": {
+    "likes": 485,
+    "stars": 944,
+    "forks": 197,
+    "views": 79332,
+    "watch": 0,
+    "comments": 182
+  },
+  "cover": {
+    "url": "https://image.lceda.cn/pullimage/cwNUVdKKMKru1Zm3GxRHOkVtJvPBbInHGOebLFTD.jpeg",
+    "path": null
+  },
+  "files": [
+    {
+      "name": "二代  2.13墨水屏单词卡全部元件及参考购买链接清单.xlsx",
+      "url": "https://image.lceda.cn/attachments/2022/10/YCexnsBhuXywlDeHuoQjw3piyFvyDLroMqswTMJv.xlsx",
+      "original_id": "c93321c4d83540899ef3cae901472780",
+      "ext": "xlsx",
+      "mime": "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet",
+      "size": 17938,
+      "md5": "7917b25354f173eaaee03e2183774763"
+    }
+  ],
+  "raw_fields": {
+    "path": "zhushengji/er-dai-dan-ci-ka",
+    "grade": 4,
+    "origin": "std",
+    "public": true,
+    "publish": true,
+    "skipped_files": []
+  }
+}