chore: add clang-tidy pre-commit hook

[Mordris]

Closes #294.

What changed

• Add a local clang-tidy hook to .pre-commit-config.yaml so the CI clang-tidy check can be run locally before pushing.
• Add scripts/run_clang_tidy.py, which the hook calls. It mirrors .github/workflows/clang_tidy.yml: only the changed C/C++ files that appear in build/compile_commands.json are analysed, using the repo .clang-tidy config and --warnings-as-errors=*.
• Files not in the compilation database — and anything under thirdparty/, build/, or the generated gen/ dirs — are skipped, matching the workflow's ignore list.
• When clang-tidy or the compilation database is unavailable the hook skips with a hint instead of blocking the commit, so contributors without a configured build are not blocked (CI stays the enforcing gate). Set ZVEC_CLANG_TIDY_STRICT=1 to make missing tooling an error; CLANG_TIDY / BUILD_DIR override the binary and build directory.

How to use

cmake -S . -B build -DCMAKE_EXPORT_COMPILE_COMMANDS=ON
pre-commit install

The hook then runs on the C/C++ files you change; commit as usual.

Validation

• pre-commit validate-config passes; scripts/run_clang_tidy.py passes the repo ruff lint and format checks.
• Verified against a real local build (cmake -S . -B build -G Ninja -DCMAKE_EXPORT_COMPILE_COMMANDS=ON -DBUILD_TOOLS=ON; compilation database with ~1.6k entries; clang-tidy 18.1.1), driven through pre-commit run clang-tidy:
  • clean upstream sources (e.g. files under src/ailego/) pass;
  • a modernize-use-nullptr violation temporarily added to a tracked source file makes the hook fail (exit 1) with the diagnostic, and passes again once reverted;
  • files under thirdparty/ and generated gen/ dirs, and files absent from the compilation database, are skipped;
  • with no build/compile_commands.json the hook skips without blocking the commit (and fails under ZVEC_CLANG_TIDY_STRICT=1).