Bound pre-commit hook reads when checking managed hook markers

[Widthdom]

Summary

Hook install/status/uninstall paths read the entire pre-commit hook file to check whether it is managed by cdidx.

Evidence

src/CodeIndex/Cli/HookCommandRunner.cs calls File.ReadAllText(ioHookPath) and IsManagedHook(File.ReadAllText(ioHookPath)) when checking existing hooks. There is no file-size cap before reading the hook into memory.

Impact

A large pre-existing hook can make hook commands allocate excessive memory or take longer than necessary, even though cdidx only needs to detect a small managed marker.

Suggested fix

Check length before reading, or stream a bounded prefix/suffix sufficient to detect the managed marker. Keep behavior distinct from the separate atomic hook swap issue.

[Widthdom]

Work started on branch fix-issue2844-2856-2857-2870-2858-2871-2872-2867.