[ci] Add local lint setup with pre-push hook to catch issues early (#4925)

* Add local lint setup with pre-push hook to catch issues early

Developers can now catch lint issues before pushing, reducing CI failures
and iteration time. The setup uses golangci-lint locally with the same
configuration as CI.

Setup:
- Run `make setup-hooks` once after cloning
- Pre-push hook automatically lints changed files (~90s)
- Use `make lint` to manually check changed files
- Use `make lint-all` to run full CI-equivalent lint

The Makefile auto-installs golangci-lint to ./bin/ using go install to
match the Go version in go.mod, avoiding version compatibility issues.

---------

Co-authored-by: mlsmaycon <mlsmaycon@gmail.com>

.githooks/pre-push

@@ -0,0 +1,11 @@
+#!/bin/bash
+
+echo "Running pre-push hook..."
+if ! make lint; then
+    echo ""
+    echo "Hint: To push without verification, run:"
+    echo "  git push --no-verify"
+    exit 1
+fi
+
+echo "All checks passed!"

CONTRIBUTING.md

@@ -136,6 +136,14 @@ checked out and set up:
    go mod tidy
    ```
 
+6. Configure Git hooks for automatic linting:
+
+   ```bash
+   make setup-hooks
+   ```
+
+   This will configure Git to run linting automatically before each push, helping catch issues early.
+
 ### Dev Container Support
 
 If you prefer using a dev container for development, NetBird now includes support for dev containers. 

Makefile

@@ -0,0 +1,27 @@
+.PHONY: lint lint-all lint-install setup-hooks
+GOLANGCI_LINT := $(shell pwd)/bin/golangci-lint
+
+# Install golangci-lint locally if needed
+$(GOLANGCI_LINT):
+	@echo "Installing golangci-lint..."
+	@mkdir -p ./bin
+	@GOBIN=$(shell pwd)/bin go install github.com/golangci/golangci-lint/cmd/golangci-lint@latest
+
+# Lint only changed files (fast, for pre-push)
+lint: $(GOLANGCI_LINT)
+	@echo "Running lint on changed files..."
+	@$(GOLANGCI_LINT) run --new-from-rev=origin/main --timeout=2m
+
+# Lint entire codebase (slow, matches CI)
+lint-all: $(GOLANGCI_LINT)
+	@echo "Running lint on all files..."
+	@$(GOLANGCI_LINT) run --timeout=12m
+
+# Just install the linter
+lint-install: $(GOLANGCI_LINT)
+
+# Setup git hooks for all developers
+setup-hooks:
+	@git config core.hooksPath .githooks
+	@chmod +x .githooks/pre-push
+	@echo "✅ Git hooks configured! Pre-push will now run 'make lint'"