fix(ci): Support docs-only changes without blocking PR merges

[kxrm]

This PR fixes the CI workflow to properly handle documentation-only changes without blocking PR merges due to missing CI status checks.

Problem

Documentation-only PRs were being blocked because:

1. The CI workflow used paths-ignore to skip docs/markdown files
2. Branch protection rules still required "CI Success" status check
3. When CI doesn't run, there's no status to check → merge blocked

Solution

• ✅ Remove paths-ignore from workflow triggers so CI always runs
• ✅ Add change detection with new check-changes job to identify docs-only PRs
• ✅ Conditional heavy jobs - test/build/security jobs only run for code changes
• ✅ Smart CI Success - validates appropriate jobs based on change type
• ✅ Maintain docs validation - docs job still runs for documentation changes

Benefits

• 📝 Documentation PRs can merge without waiting for unnecessary code tests
• 🔧 Code PRs still get full CI validation
• ⚡ Faster CI for docs-only changes while maintaining protection
• 🛡️ Branch protection rules work correctly for both change types

Testing

This change enables the documentation PR (#40) to complete CI and merge successfully.

Closes #40 (indirectly by unblocking documentation PRs)