feat: add version flag and Makefile for release builds

- Add -version flag to show build version
- Add Makefile with build targets:
  - make build-release: optimized build with version
  - make build-all: cross-compile for Linux/macOS
  - make run/test/clean: dev commands
- Update documentation with build commands
- Version is embedded via ldflags during build

Usage:
  make build-release  # Build with version
  ./bin/qfs -version  # Show version

Version format: v0.2.5-1-gfa0f5e3 (tag-commits-hash)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

CLAUDE.md

@@ -134,9 +134,22 @@ Go 1.22+ | Gin | GORM | MariaDB 11 | SQLite (glebarez/sqlite) | htmx + Tailwind
 
 ## Commands
 ```bash
-go run ./cmd/qfs          # Dev server
-go run ./cmd/cron -job=X     # cleanup-pricelists | update-prices | update-popularity
-CGO_ENABLED=0 go build -ldflags="-s -w" -o bin/qfs ./cmd/qfs
+# Development
+go run ./cmd/qfs                # Dev server
+make run                        # Dev server (via Makefile)
+
+# Production build
+make build-release              # Optimized build with version (recommended)
+VERSION=$(git describe --tags --always --dirty)
+CGO_ENABLED=0 go build -ldflags="-s -w -X main.Version=$VERSION" -o bin/qfs ./cmd/qfs
+
+# Cron jobs
+go run ./cmd/cron -job=cleanup-pricelists  # Remove old unused pricelists
+go run ./cmd/cron -job=update-prices       # Recalculate all prices
+go run ./cmd/cron -job=update-popularity   # Update popularity scores
+
+# Check version
+./bin/qfs -version
 ```
 
 ## Code Style