docs: rewrite README as modern Jib drop-in replacement landing page

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

Author: jbadeau

.gitignore

@@ -13,6 +13,7 @@
 # Test output
 *.tar
 /output/
+coverage*.out
 
 # Build cache
 /dist/