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/2f01fdb9fbaf499f8b537081ce3e4a66/_urls.json

@@ -0,0 +1,11 @@
+{
+  "detail_url": "https://oshwhub.com/z_star/zynq7020-core-board-and-various-rf-modules",
+  "cover_url": "https://image.lceda.cn/pullimage/kIcEEUbe0wdv3WwOSfGTZD6PCBvrU3Zomxe6voan.jpeg",
+  "attachments": [
+    {
+      "name": "ZYNQ从FLASH启动RGB灯程序.mp4",
+      "url": "https://image.lceda.cn/attachments/2024/1/EoyKqr4QvaBtKuGN1IvKzJkhlaERv4ieQOjj7hCf.mp4",
+      "original_id": "2fa7c8f1e02848d0a48c5eb377b015f6"
+    }
+  ]
+}

data/raw/oshwhub/2f01fdb9fbaf499f8b537081ce3e4a66/description.md

@@ -0,0 +1,9 @@
+# ZYNQ7020核心板及各种射频模块
+
+ZYNQ7020核心板（主体，最低成本仅需90元！）、170MSPSADC、210MSPSDAC、1.6GSPS 16bit DAC、9GHz PLL、500MSPS 12bit ADC等
+
+---
+- Source: https://oshwhub.com/z_star/zynq7020-core-board-and-various-rf-modules
+- Author: 上电冒烟 (z_star)
+- License: CC BY 3.0
+- Published: 2024-01-25T15:57:56.000Z

data/raw/oshwhub/2f01fdb9fbaf499f8b537081ce3e4a66/metadata.json

@@ -0,0 +1,50 @@
+{
+  "source": "oshwhub",
+  "source_url": "https://oshwhub.com/z_star/zynq7020-core-board-and-various-rf-modules",
+  "project_id": "2f01fdb9fbaf499f8b537081ce3e4a66",
+  "title": "ZYNQ7020核心板及各种射频模块",
+  "description_short": "ZYNQ7020核心板（主体，最低成本仅需90元！）、170MSPSADC、210MSPSDAC、1.6GSPS 16bit DAC、9GHz PLL、500MSPS 12bit ADC等",
+  "description_path": "description.md",
+  "author": {
+    "username": "z_star",
+    "display_name": "上电冒烟",
+    "user_id": "63725c4e64e5478099fa821cabcea5b5"
+  },
+  "license": "CC BY 3.0",
+  "tags": [],
+  "created_at": "2024-01-13T04:25:36.000Z",
+  "updated_at": "2025-12-19T01:07:08.000Z",
+  "published_at": "2024-01-25T15:57:56.000Z",
+  "crawled_at": "2026-04-28T17:27:31.891283+00:00",
+  "metrics": {
+    "likes": 599,
+    "stars": 1139,
+    "forks": 0,
+    "views": 98534,
+    "watch": 0,
+    "comments": 233
+  },
+  "cover": {
+    "url": "https://image.lceda.cn/pullimage/kIcEEUbe0wdv3WwOSfGTZD6PCBvrU3Zomxe6voan.jpeg",
+    "path": null
+  },
+  "files": [
+    {
+      "name": "ZYNQ从FLASH启动RGB灯程序.mp4",
+      "url": "https://image.lceda.cn/attachments/2024/1/EoyKqr4QvaBtKuGN1IvKzJkhlaERv4ieQOjj7hCf.mp4",
+      "original_id": "2fa7c8f1e02848d0a48c5eb377b015f6",
+      "ext": "mp4",
+      "mime": "video/mp4",
+      "size": 25222219,
+      "md5": "f618054866a257be44e702e4e4d9cb5e"
+    }
+  ],
+  "raw_fields": {
+    "path": "z_star/zynq7020-core-board-and-various-rf-modules",
+    "grade": 4,
+    "origin": "pro",
+    "public": true,
+    "publish": true,
+    "skipped_files": []
+  }
+}