chore(dev): add pre-commit validation hooks

Add the same pre-commit validation surface used by solverforge-hospital.

The hook set checks YAML, merge conflicts, file endings, trailing whitespace, large files, gitleaks, rustfmt, and clippy. This is development tooling only: it does not affect runtime behavior, solver configuration, route rendering, or the browser app.

.pre-commit-config.yaml

@@ -0,0 +1,21 @@
+repos:
+-   repo: https://github.com/pre-commit/pre-commit-hooks
+    rev: v4.5.0
+    hooks:
+    -   id: check-yaml
+    -   id: end-of-file-fixer
+    -   id: trailing-whitespace
+    -   id: check-merge-conflict
+    -   id: check-added-large-files
+
+-   repo: https://github.com/gitleaks/gitleaks
+    rev: v8.18.0
+    hooks:
+    -   id: gitleaks
+-   repo: https://github.com/doublify/pre-commit-rust
+    rev: v1.0
+    hooks:
+    -   id: fmt
+        args: ["--", "--check"]
+    -   id: clippy
+        args: ["--", "-D", "warnings"]