feat: add Dockerfile validation to pre-commit hooks

Added custom Dockerfile validation script that detects mismatches between
base image OS (Debian vs Alpine) and package managers (apt vs apk).

This will catch errors like:
- Using golang:latest (Debian) with apk commands
- Using alpine images with apt commands

The hook runs automatically on commit and would have caught the recent
golang:latest + apk mismatch that caused Docker build failures.

.pre-commit-config.yaml

@@ -27,3 +27,11 @@ repos:
         exclude: '^(frontend/(coverage|dist|node_modules|\.vite)/|.*\.tsbuildinfo$)'
       - id: check-yaml
       - id: check-added-large-files
+  - repo: local
+    hooks:
+      - id: dockerfile-check
+        name: dockerfile validation
+        entry: tools/dockerfile_check.sh
+        language: script
+        files: "Dockerfile.*"
+        pass_filenames: true