[CK] Add project root marker for monorepo compatibility
(#4430)
## Summary
- Add `.ck-project-root` marker file at the composablekernel project
root
- Update `find_project_root()` in `script/tools/common.sh` to look for
this marker instead of `.git`
- Fixes project root detection when CK is part of the rocm-libraries
monorepo
## Background
Since the project was moved into the monorepo, the `.git` directory is
at the monorepo root rather
than the CK project root. This caused `find_project_root()` to return
the wrong path, breaking tools
in `script/tools/`.
## Test plan
- [x] Verify `find_project_root` returns correct path from any CK
subdirectory
- [x] Verify `ck-build --help` works
- [x] Verify `ck-configure --help` works
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: Thomas Ning <Thomas.Ning@amd.com>
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