Add ShellCheck to CI

[scal444]

Implements #151

[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge, with no outstanding correctness or repository-rule violations identified.

Summary

• Installs an integrity-checked ShellCheck 0.11.0 binary in the lint workflow.
• Adds a repository-wide ShellCheck runner for tracked .sh and .bash files.
• Improves quoting and null-safe file traversal across administration scripts.
• Allows clang-tidy to continue when the optional LLVM symbolizer is unavailable.

_{Reviews (2) · Last reviewed commit: "Keep LLVM symbolizer optional in clang-t..."}

[evasnow1992]

With set -e on line 20, this now aborts the whole script if llvm-symbolizer-17 isn't installed. Looks like LLVM_SYMBOLIZER_PATH isn't read anywhere in this script. Do we really require it to be installed?

[scal444]

Fixed. It's optional

[evasnow1992]

Changes look good to me.