feat(etl-api): validate unsupported column types

[aleksandarskrbic]

What kind of change does this PR introduce?

Fixes #34

What is the new behavior?

Added:

• Request validation for publication creation and updates. Publications now validate that names and table schemas/names are not empty or whitespace-only.
• Validation to prevent publications with unsupported PostgreSQL column types (like custom enums).
• Test suite covering all publication CRUD operations, validation edge cases, and unsupported column type scenarios.

[iambriccardo]

@codex review

[iambriccardo]

Thanks for the contribution, I will review it as soon as I get to it!

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

delete_publication_succeeds never sets up a valid publication

This test now builds a publication request with tables: vec![], but the new validate_publication helper rejects empty table lists (lines 319‑340 in the handler), so the setup call returns 400 and no publication is created. Because delete_publication issues DROP PUBLICATION IF EXISTS, the delete and subsequent 404 read both succeed even when deletion of an existing publication is broken, so the test no longer exercises the real success path. Populate the publication with at least one table before deleting so the scenario is meaningful.

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