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/91fd41224cd74ffd8410bc77b216693b/metadata.json

@@ -0,0 +1,68 @@
+{
+  "source": "oshwhub",
+  "source_url": "https://oshwhub.com/esp-college/esp-sparkbot",
+  "project_id": "91fd41224cd74ffd8410bc77b216693b",
+  "title": "ESP-SparkBot",
+  "description_short": "ESP-SparkBot 基于 ESP32-S3，融合语音交互、图像识别与多媒体娱乐，可变身遥控小车、玩转本地 AI，支持大模型对话、实时视频传输和高清视频投屏，性能强大，乐趣无限！",
+  "description_path": "description.md",
+  "author": {
+    "username": "esp-college",
+    "display_name": "乐鑫小铁匠",
+    "user_id": "16555ec60452466ea4dbaa7c6b92cd89"
+  },
+  "license": "GPL 3.0",
+  "tags": [],
+  "created_at": "2024-10-15T03:45:10.000Z",
+  "updated_at": "2025-11-11T10:24:51.000Z",
+  "published_at": "2025-03-12T05:42:19.000Z",
+  "crawled_at": "2026-04-28T16:59:54.198797+00:00",
+  "metrics": {
+    "likes": 837,
+    "stars": 2135,
+    "forks": 0,
+    "views": 304205,
+    "watch": 0,
+    "comments": 343
+  },
+  "cover": {
+    "url": "https://image.lceda.cn/pullimage/YyPkhuGTNedxg6yM3fkJBovQB2b56pCCJb27zQjN.png",
+    "path": "cover.png"
+  },
+  "files": [
+    {
+      "name": "ESP-Sparkbot V1.0 版本 3D 结构文件.zip",
+      "url": "https://image.lceda.cn/oshwhub/project/attachments/d0d0ef3b19cf40e8b73c83f81aa328b4.zip",
+      "original_id": "019b2563c2af4ec39f6ac69d38f47f02",
+      "ext": "zip",
+      "mime": "application/x-zip-compressed",
+      "size": 4435050,
+      "md5": "5a8a03e419e6698a90675c52cfa79b0b"
+    },
+    {
+      "name": "sparkbot 主体头部后壳（有开关版本）_20250107.STL",
+      "url": "https://image.lceda.cn/oshwhub/project/attachments/796bd6cff4b444c999a75c38063ede51.stl",
+      "original_id": "c24d5e2146234f408cbd6ed081f4ea39",
+      "ext": "stl",
+      "mime": "application/octet-stream",
+      "size": 13559984,
+      "md5": "d01d20c398e3950af6e8ef1107b390ff"
+    },
+    {
+      "name": "esp-sparkbot 配件 3D 模型.zip",
+      "url": "https://image.lceda.cn/oshwhub/project/attachments/0e4e4896bca64ea88202a15658463edc.zip",
+      "original_id": "5fd4991602a54136aad5c0d1cab2d6e2",
+      "ext": "zip",
+      "mime": "application/x-zip-compressed",
+      "size": 1344016,
+      "md5": "4192a0f84a48de1d02efa937afaf69bb"
+    }
+  ],
+  "raw_fields": {
+    "path": "esp-college/esp-sparkbot",
+    "grade": 3,
+    "origin": "pro",
+    "public": true,
+    "publish": true,
+    "skipped_files": []
+  }
+}