chore: rename @pgsql/transform to @pgsql/transform-ast

[pyramation]

Summary

Step 1 of constructive-io/constructive-planning#1271: frees the @pgsql/transform npm name so constructive-db's transform-schemas (SQL schema transform / facts / closure layer) can move in under it.

• packages/transform → packages/transform-ast; package renamed @pgsql/transform → @pgsql/transform-ast, version 18.1.1 → 18.2.0 (same 18.x major, minor bump only — code unchanged, pure rename).
• Updated references: root README.md / AGENTS.md package tables, .agents/skills/* docs, CI package matrix in run-tests.yaml, package READMEs (including @pgsql/transform/transformers-direct/... import paths → @pgsql/transform-ast/...), and the pnpm-lock.yaml importer key (minimal 1-line edit to avoid pnpm rewrite churn).
• No in-repo consumers existed (pgsql-parser/pgsql-deparser/CLI don't depend on it), so nothing else changes.

Verified: pnpm install --frozen-lockfile (pnpm 9 / node 20, matching CI), full build, and the package's full test suite (1437 tests) pass.

After merge/publish: npm deprecate the old @pgsql/transform versions with a pointer to @pgsql/transform-ast, then land the transform-schemas move as the new @pgsql/transform (next PR).

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

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