Add linting documentation and pre-commit hooks (#177)

## Summary

This PR improves the developer experience by adding clear linting
documentation and optional pre-commit hooks to catch issues before CI.
Helpful to avoid fighting Claude Code / Copilot on "please make sure
linting passes CI".

## Changes

- Updated `README.md` with:
  - Go 1.23.x requirement (was "1.18 or later")
  - golangci-lint v1.61.0 in prerequisites
  - New Development section with linting instructions
  
- Updated `CLAUDE.md` with:
  - Development Setup section
  
- Added `.githooks/pre-commit`:
  - Runs golangci-lint and gofmt checks
  - References README for installation instructions
  - Can be bypassed with `--no-verify` when needed

## Test Plan

- [x] Verified pre-commit hook blocks commits when golangci-lint is
missing
- [x] Confirmed hook shows clear error message pointing to README
- [x] Tested that linting passes with Go 1.23.0 and golangci-lint
v1.61.0
- [x] Verified gofmt correctly identifies formatting issues

Co-authored w/ Claude Code

---------

Co-authored-by: Charles Lowell <10964656+chlowell@users.noreply.github.com>

.githooks/pre-commit

@@ -0,0 +1,35 @@
+#!/bin/bash
+
+# Pre-commit hook for MCP Registry
+# Runs linting and formatting checks before allowing commits
+
+set -e
+
+echo "Running pre-commit checks..."
+
+# Check if golangci-lint is installed
+if ! command -v golangci-lint &> /dev/null; then
+    echo "❌ golangci-lint is not installed!"
+    echo "See README.md Prerequisites section for installation instructions."
+    exit 1
+fi
+
+# Run golangci-lint
+echo "Running golangci-lint..."
+if ! golangci-lint run --timeout=5m; then
+    echo "❌ Linting failed! Please fix the issues above."
+    exit 1
+fi
+
+# Check formatting
+echo "Checking Go formatting..."
+UNFORMATTED=$(gofmt -s -l .)
+if [ -n "$UNFORMATTED" ]; then
+    echo "❌ The following files need formatting:"
+    echo "$UNFORMATTED"
+    echo ""
+    echo "Run 'gofmt -s -w .' to fix formatting issues."
+    exit 1
+fi
+
+echo "✅ All pre-commit checks passed!"