Normalize YAML export formatting for repo-backed namespaces

[shangyian]

Summary

The YAML files generated through the UI (e.g., when creating a node on a branch) are now formatted identically to files written by hand in various repos that use yamlfix as a pre-commit hook. Previously, the server's ruamel.yaml output could diverge from what yamlfix (used as a pre-commit hook in deployment repos) would produce, causing spurious diffs on the first commit.

List fields (owners, tags, column attributes) were also serialized in arbitrary order, producing non-deterministic output across server restarts or DB query reorderings.

The fix sorts owners, tags, and column attributes alphabetically before serialization, then runs yamlfix (already a server dependency) on the output with explicit_start=False and line_length=120, matching the standard repo config. Short lists now render inline (tags: [abc, def]) and multiline queries retain |- block style.

Test Plan

• PR has an associated issue: #
• make check passes
• make test shows 100% unit test coverage

Deployment Plan

[netlify]

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