fix: address code review findings

- Create README.md with project overview, quick start, Docker deployment, CI/CD info
- Update CLAUDE.md with Deployment section
- Fix cmd/api/main.go to use REDIS_ADDR env var with fallback
- Fix Dockerfile to use golang:1.22-alpine instead of golang:1.26-alpine
- Fix .gitea/workflows/deploy.yml to include Docker registry prefix in image tags

Dockerfile

@@ -1,5 +1,5 @@
 # Builder stage
-FROM golang:1.26-alpine AS builder
+FROM golang:1.22-alpine AS builder
 
 WORKDIR /app