feat: log coglet build info and SDK version at startup (#2829)
* feat: log coglet build info and SDK version at startup
Print coglet version, git sha, dirty flag, build time, and debug/release
mode to logs on boot. Also log cog SDK and Python versions.
Expose git_sha and build_time in the /health-check response so running
containers can be identified without log access.
Add COGLET_GIT_DIRTY to build.rs and track .git/index for rebuild on
staging changes.
* refactor: rename 'cog' to 'python_sdk' in VersionInfo
Align with naming convention: 'cog' is the suite, 'coglet' is the
in-container server, 'python_sdk' is the SDK models are built on.
* fix: clean:go now removes dist/go/, add build summary
clean:go was removing ./cog (legacy path) but build:cog outputs to
dist/go/*/cog, so 'mise clean && mise build' left a stale CLI binary.
Also add a _build_summary task that prints artifact paths and versions
after 'mise build'.
* fix: update test assertion to match renamed python_sdk version field
