ci: bump pinned mdsmith baseline to v0.29.0 (#451)

Update the compatibility-baseline binary installed across CI and
merge-queue workflows from v0.28.0 to v0.29.0. The pinned SHA256 is
the published checksum of the v0.29.0 mdsmith-linux-amd64 asset
(verified against the release checksums.txt).

https://claude.ai/code/session_01UXMYUjKeZr98A7p3q4dyWZ

Co-authored-by: Claude <noreply@anthropic.com>

Author: jeduden

.github/actions/setup-mdsmith-pinned-version/action.yml

@@ -10,8 +10,8 @@ runs:
       env:
         # Pinned compatibility baseline for mdsmith release checks and merge tooling.
         # Bump here only when intentionally updating that baseline.
-        MDSMITH_VERSION: v0.28.0
-        MDSMITH_SHA256: 62870ea2fd0681dd42ef4c43cf1760a035949fa51592e52ed16575386828b6a7
+        MDSMITH_VERSION: v0.29.0
+        MDSMITH_SHA256: 130d784cec7fe096ba332974dcd615fc3b4a0ca479730c5fd5a3c9f1f1f55bd3
       # The binary is downloaded over HTTPS and SHA256-verified above
       # before $HOME/.local/bin is appended to PATH, so the github-env
       # write is safe to ignore.