feat: improve HTML report with fix plan details, scan notes, and search

[sonukapoor]

Brings the HTML report closer to parity with verbose terminal output, and adds interactive search.

• Breaking change indicator (⚠ breaking badge) on fix targets where the recommended version is a major bump
• Versions scanned and still-vulnerable counts shown under each fix command
• Fix version adjustment notes shown inline when a recommended version was adjusted
• Scan notes and warnings collapsed into a single toggleable 'Scan notes (N)' box below the fix plan — informational, out of the way
• Suggested Fix Plan is now the first thing visible after the severity summary
• Search input in the findings header filters across package name, version, and CVE/advisory IDs as you type, works in combination with the existing severity filter buttons

Closes #230