feat(reference-curator): add --wayback-fallback flag + CAPTCHA/IP block detection

- Add _is_captcha_response() to detect Google sorry page, 429, and
  "unusual traffic" markers in crawler responses
- Add --wayback-fallback CLI flag: auto-switches remaining URLs to
  web.archive.org/web/2024/ after 3 consecutive CAPTCHA blocks
- Add --delay CLI flag for polite crawling with configurable interval
- Add retry logic with exponential backoff on 429/5xx responses
- Document GOTCHA section in crawler CLAUDE.md with detection signals,
  Wayback detour solution, and prevention tips
- Add GOTCHA callout in pipeline orchestrator Stage 2 docs
- Record source: wayback in frontmatter for traceability

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

custom-skills/90-reference-curator/07-pipeline-orchestrator/code/CLAUDE.md

@@ -100,12 +100,22 @@ If mode == 'topic':
 
 ### Stage 2: Web Crawler
 ```
-→ Claude uses Firecrawl MCP tools
+→ Claude uses Firecrawl MCP tools or seo_crawler_adapter.py
 → crawl_mgr.py store-result
 → If --save-raw or --no-distill: write raw .raw.md files to output
 → pipeline.py advance --stage storing
 ```
 
+**⚠️ GOTCHA — IP Block / CAPTCHA Detour:**
+If the crawl stage encounters persistent 429 or CAPTCHA responses (e.g., Google's `google.com/sorry/` redirect), the pipeline should **NOT** retry indefinitely. Instead:
+1. Detect: 3+ consecutive 429/CAPTCHA responses = IP blocked
+2. Detour: Re-invoke `seo_crawler_adapter.py` with `--wayback-fallback` flag
+3. The crawler auto-switches remaining URLs to `web.archive.org/web/2024/{url}`
+4. Frontmatter records `source: wayback` for traceability
+5. Resume normal pipeline from Stage 3
+
+**Common triggers:** Large-volume crawls (>50 pages) on `support.google.com`, `developer.mozilla.org`, or any site with aggressive bot detection. **Prevention:** Always use `--delay 2.0` or higher for these domains.
+
 ### Stage 3: Content Repository
 ```
 → repo.py store (for each crawled doc)