feat: initialize project structure and dependencies

- Initialize Go module with all required dependencies
- Add Makefile with build targets (all, frontend, build, clean, test, run, build-linux, build-windows)
- Create main.go skeleton with CLI flags (--addr, --data, --init)
- Add README.md with project overview and usage instructions
- Add .gitignore for bin, data, and build artifacts

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Makefile

@@ -0,0 +1,24 @@
+.PHONY: all build frontend clean test run build-linux build-windows
+
+all: frontend build
+
+frontend:
+	cd web && npm install && npm run build
+
+build:
+	go build -o bin/gitm .
+
+clean:
+	rm -rf bin/ web/dist/ web/node_modules/
+
+test:
+	go test -v ./...
+
+run:
+	go run main.go
+
+build-linux:
+	GOOS=linux GOARCH=amd64 go build -o bin/gitm-linux .
+
+build-windows:
+	GOOS=windows GOARCH=amd64 go build -o bin/gitm.exe .