Add link topology and asset analysis modules

New check modules for comprehensive site analysis:

topology.rs - Link spidering (depth 1)
- Discover same-origin links from <a> and <link> elements
- Fetch sitemap.xml for additional URLs
- Probe discovered URLs with HEAD requests
- Build site structure tree from paths
- Detect broken links (4xx/5xx responses)
- Configurable via --max-urls flag (default: 50)

assets.rs - Asset analysis with timing
- Extract assets: scripts, stylesheets, images, fonts, media
- Full timing breakdown per asset (DNS, TCP, TLS, TTFB)
- Classify provenance: same-origin, subdomain, known CDN, third-party
- Size and cache header analysis
- Lighthouse-style recommendations for slow/large assets
- Configurable via --max-assets flag (default: 50)

CLI updates:
- Add --max-urls, --max-assets flags
- Add --skip-topology, --skip-assets flags
- Add --only flag for running specific checks only
- Update pretty and compact output formats

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: raffaelschneider

src/checks.rs

@@ -9,3 +9,5 @@ pub mod techstack;
 pub mod seo;
 pub mod aeo;
 pub mod content;
+pub mod topology;
+pub mod assets;