docs: Add CI status, coverage, and Go Report Card badges to README

- Added CI status badge (GitHub Actions)
- Added coverage badge (from coverage.json)
- Added Go Report Card badge

Coverage badge shows 80.6% coverage across all packages.

1 files changed, 4 insertions, 0 deletions

diff --git a/README.md b/README.md
index 9f4de3e..2c40674 100644
--- a/README.md
+++ b/README.md
@@ -1,5 +1,9 @@
 # gt
 
+[![CI](https://github.com/snonux/gt/actions/workflows/ci.yml/badge.svg)](https://github.com/snonux/gt/actions/workflows/ci.yml)
+[![Coverage](https://img.shields.io/endpoint?url=https://raw.githubusercontent.com/snonux/gt/refs/heads/main/coverage.json)](https://github.com/snonux/gt/actions/workflows/ci.yml)
+[![Go Report Card](https://goreportcard.com/badge/codeberg.org/snonux/perc)](https://goreportcard.com/report/codeberg.org/snonux/perc)
+
 A simple AI-engineered command-line percentage calculator written in Go.
 
 ## Rational Number Mode (Optional)