Fix _zz_logs.sh / _zz_log.sh naming mismatch in common-utils

[tomgrv]

Problem

.github/instructions/repo.instructions.md documents a known workaround:

_zz_logs.sh: No such file — caused by install.sh line 9 typo: _zz_logs vs _zz_log — fixed by ln -sf src/common-utils/_zz_log.sh src/common-utils/_zz_logs.sh

This means there's a real naming mismatch between what's referenced (_zz_logs.sh) and what actually exists (_zz_log.sh) in src/common-utils, currently "fixed" only by a manual symlink step documented as setup folklore rather than a real source fix.

Proposal

• Find the actual reference to _zz_logs (likely in install.sh or a script under src/common-utils) and either rename the source file to match, or fix the reference to use the correct existing filename — whichever is the actual intended name.
• Remove the manual symlink workaround from .github/instructions/repo.instructions.md once the real fix lands, since it should no longer be necessary.

Where this lives / sync note

The fix belongs in src/common-utils (the actual source of _zz_log.sh and whatever references it). Since common-utils is depended on by most other features and is itself split out to its own repo via split-monorepo.yml, fixing it at the source here is what propagates the fix everywhere — the symlink workaround should not be needed by any consumer once this is fixed upstream.

Acceptance criteria

• No script in the repo or any feature needs the manual ln -sf workaround to run successfully.
• The workaround note is removed from .github/instructions/repo.instructions.md.