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/da55d50b394b4553bbcb799dc27a7e63/metadata.json

@@ -0,0 +1,77 @@
+{
+  "source": "oshwhub",
+  "source_url": "https://oshwhub.com/no_chicken/zhi-neng-shou-biao-OV-Watch_V2.2",
+  "project_id": "da55d50b394b4553bbcb799dc27a7e63",
+  "title": "智能手表OV-Watch",
+  "description_short": "功能包括日历、计算器、秒表、NFC、蓝牙无线升级、与手机传信息、抬腕亮屏、心率检测、环境温湿度检测、指南针、海拔测量等功能。已经尽量满足现在智能手表的功能，后期大家可以继续添加修改很多东西~",
+  "description_path": "description.md",
+  "author": {
+    "username": "no_chicken",
+    "display_name": "不吃油炸鸡",
+    "user_id": "f7bcdbf6b47c41bdb9ee2f15c10033a9"
+  },
+  "license": "CC BY-NC-SA 4.0",
+  "tags": [],
+  "created_at": "2023-05-06T12:09:09.000Z",
+  "updated_at": "2026-03-20T10:38:26.000Z",
+  "published_at": "2025-12-29T03:42:25.000Z",
+  "crawled_at": "2026-04-28T16:59:33.089740+00:00",
+  "metrics": {
+    "likes": 1397,
+    "stars": 3422,
+    "forks": 0,
+    "views": 361711,
+    "watch": 0,
+    "comments": 374
+  },
+  "cover": {
+    "url": "https://image.lceda.cn/oshwhub/pullImage/532f00b2d581404bbce37aedaa31ab45.jpeg",
+    "path": "cover.jpeg"
+  },
+  "files": [
+    {
+      "name": "配件采购清单.pdf",
+      "url": "https://image.lceda.cn/oshwhub/project/attachments/f8a0e501e4fd4daaa41d659456bf017e.pdf",
+      "original_id": "a29ef358dfca4ae3ac2c8d65df612ddc",
+      "ext": "pdf",
+      "mime": "application/pdf",
+      "size": 565334,
+      "md5": "84e4dfde8cde975f57044a9485002513"
+    },
+    {
+      "name": "过孔焊接演示.mp4",
+      "url": "https://image.lceda.cn/oshwhub/project/attachments/053616d8dea940649409ce5da4a0fe4a.mp4",
+      "original_id": "5c94a96f2b7f41839ddbfcd33c0b991f",
+      "ext": "mp4",
+      "mime": "video/mp4",
+      "size": 95827826,
+      "md5": "7002cbaaaaf5adcb1764381766c8469a"
+    },
+    {
+      "name": "LVGL仿真lv_sim_vscode_win.rar",
+      "url": "https://image.lceda.cn/oshwhub/project/attachments/672b20d4e8cf4e0c915c2e7027273971.rar",
+      "original_id": "76986c4512614a12bbe45abb599a0979",
+      "ext": "rar",
+      "mime": "application/octet-stream",
+      "size": 35474717,
+      "md5": "71549346b901a11aa53f60b692f8fadb"
+    },
+    {
+      "name": "手表装配与OTA升级.mp4",
+      "url": "https://image.lceda.cn/oshwhub/project/attachments/90dbfda3f701468b8d70318ff91dd58d.mp4",
+      "original_id": "debbb17d919d40098946e4ec1f70a8db",
+      "ext": "mp4",
+      "mime": "video/mp4",
+      "size": 187052097,
+      "md5": "82da37e1376f28f7bc259a0d8bd3f839"
+    }
+  ],
+  "raw_fields": {
+    "path": "no_chicken/zhi-neng-shou-biao-OV-Watch_V2.2",
+    "grade": 4,
+    "origin": "pro",
+    "public": true,
+    "publish": true,
+    "skipped_files": []
+  }
+}