chore(ci): add schema validation workflow

[sakinaroufid]

Description

Adds a CI workflow (schema-validation.yml) that validates schemas and ensures generated/schema-types.ts stays in sync with the source schemas on every push and PR.

This also fixes a bug in generate_ts_schema_types.js where SOURCE_ROOT was set to 'spec' (a directory that doesn't exist), causing the generator to find 0 schemas and produce a stale output. The correct path is 'source'.

The new workflow:

• Installs Node.js dependencies and ucp-schema
• Runs ucp-schema lint source/ to validate schemas
• Runs node generate_ts_schema_types.js and checks git diff --exit-code to catch desynchronized types

Note for reviewers: The large diff in generated/schema-types.ts is machine output from the generator path fix — no manual edits. Only schema-validation.yml (75 lines) and the one-line fix in generate_ts_schema_types.js need review.

This is part 1 of 3 from #13, split per maintainer request.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

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Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• My changes generate no new warnings
• New and existing unit tests pass locally with my changes