scaffold: React 19 + Spring Boot 3.4 + PostgreSQL project

Sets up toolchain pinning, format/lint (Biome + Spotless), lefthook
pre-commit hooks, Docker Compose for Postgres, and trivial passing
tests for both stacks.

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

.mise.toml

@@ -0,0 +1,27 @@
+[tools]
+java = "temurin-21"
+maven = "3.9.9"
+node = "22"
+lefthook = "1.11.12"
+gitleaks = "8.26.0"
+
+[tasks.setup]
+description = "Install deps and git hooks"
+run = """
+#!/bin/bash
+set -e
+npm --prefix frontend install
+lefthook install
+cp -n .env.example .env 2>/dev/null || true
+"""
+
+[tasks.check]
+description = "Format-check, lint, and test"
+run = """
+#!/bin/bash
+set -e
+mvn -f backend/pom.xml spotless:check -q
+(cd frontend && npx biome check src)
+mvn -f backend/pom.xml test -q
+(cd frontend && npx vitest run)
+"""