Add CLI doctor command for AI crawler access

[GHX5T-SOL]

Summary

• add aeorank doctor <url> to report robots.txt access, target HEAD status, and /llms.txt HEAD status for each crawler in the core AI_CRAWLERS list
• flag common bot-mitigation signals from cf-mitigated and x-amzn-waf-action, plus access-control status codes, without treating 404 /llms.txt or 405 HEAD responses as blocks
• add human and JSON output, mocked fetch coverage, and a docs page/sidebar entry

Fixes #5.

Validation

• pnpm install --frozen-lockfile
• pnpm --filter @aeorank/core build
• pnpm exec biome check packages/cli/src/commands/doctor.ts packages/cli/src/__tests__/doctor.test.ts packages/cli/src/index.ts apps/docs/astro.config.mjs apps/docs/src/content/docs/cli/doctor.md
• pnpm --filter aeorank-cli exec vitest run src/__tests__/doctor.test.ts -> 4 passed
• pnpm --filter aeorank-cli test -> 81 passed
• pnpm --filter aeorank-cli build
• pnpm --filter @aeorank/docs build
• node packages/cli/dist/index.js doctor https://aeorank.dev --format json --timeout 8000 -> pass, blocked []
• node packages/cli/dist/index.js doctor https://vercel.com --format json --timeout 8000 -> pass, blocked []
• node packages/cli/dist/index.js doctor https://stripe.com --format json --timeout 8000 -> pass, blocked []
• git diff --check HEAD~1 HEAD
• git show --format= --patch HEAD | gitleaks stdin --no-banner --redact

Notes

• I did not count pnpm lint as a clean gate because it currently reports pre-existing repo-wide formatting/generated .astro diagnostics and existing packages/vitepress/src/plugin.ts any diagnostics outside this diff.
• I did not count pnpm --filter aeorank-cli typecheck as a clean gate because it currently fails on existing CLI Node typing and definite-assignment issues in files such as compare.ts and scan.ts.
• AI-assisted contribution disclosure: I used OpenAI Codex to inspect the issue, make the focused code/test/docs changes, and run the checks above. I reviewed the resulting diff before submission.