refactor(transform): keep @pgsql/transform pure AST-level; move change-aware pieces up

[pyramation]

Summary

Layering fix agreed after #316/#317: this repo has no notion of pgpm "changes", so @pgsql/transform keeps only the pure AST-level surface — transformSql, qualifyUnqualified, classifyStatements facts, and round-trip validation.

Removed (with their tests): categorize.ts (CategoryProfile / TIER_PROFILE / buildCategoryOf — keyed by change name) and fixture-closure.ts (resolveFixtureClosure — takes changes + plan dependencies). They move up to a new @pgpmjs/transform package in constructive-io/constructive, which will be a superset: export * from '@pgsql/transform' plus the change-aware layer (categorize, fixture-closure, bundle-driver from the closed #317).

160 tests still pass. Tracked in constructive-io/constructive-planning#1271.

Link to Devin session: https://app.devin.ai/sessions/1aa52746e60c4df38ef2678d168269b9
Requested by: @pyramation

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