Improve local setup and Maven wrapper

.mise.toml

@@ -6,15 +6,38 @@ lefthook = "1.11.12"
 gitleaks = "8.26.0"
 
 [tasks.setup]
-description = "Install deps and git hooks"
+description = "Install deps, git hooks, env file, and validate local toolchain"
 run = """
 #!/bin/bash
-set -e
+set -euo pipefail
+
+if ! command -v java >/dev/null 2>&1; then
+  echo "ERROR: Java 21 JDK not found. Run 'mise install' first, or install OpenJDK 21 and set JAVA_HOME." >&2
+  exit 1
+fi
+
+java_major="$(java -XshowSettings:properties -version 2>&1 | awk -F= '/java.specification.version/ { gsub(/[[:space:]]/, "", $2); print $2; exit }')"
+if [ "${java_major}" != "21" ]; then
+  echo "ERROR: Java 21 is required, but found Java ${java_major}. Run 'mise install' or set JAVA_HOME to a Java 21 JDK." >&2
+  exit 1
+fi
+
+# Prime and validate the Maven wrapper cache so backend startup does not fail later.
+backend/mvnw -f backend/pom.xml -v >/dev/null
+
 npm --prefix frontend install
 lefthook install
 cp -n .env.example .env 2>/dev/null || true
 """
 
+[tasks.backend]
+description = "Run the Spring Boot backend"
+run = "backend/mvnw -f backend/pom.xml spring-boot:run"
+
+[tasks.frontend]
+description = "Run the Vite frontend"
+run = "npm --prefix frontend run dev"
+
 [tasks.check]
 description = "Format-check, lint, and test"
 run = """