feat(pgpm-core): renameChanges — atomic change rename/move across files, headers, and plan

[pyramation]

Summary

Atom 3 of the schema-transform platform plan (constructive-planning #1226, builds on the Atom 1 header model): a first-class rename/move primitive for pgpm changes in new pgpm/core/src/refactor/rename.ts, exported from @pgpmjs/core.

A rename is a coupled 4-way rewrite, now done atomically by renameChanges(moduleDir, renames, { dryRun? }):

1. move deploy|revert|verify/<change>.sql files (creating dirs, pruning emptied ones)
2. rewrite the moved scripts' own header identity (-- Deploy [project:]change[ to pg]) via renameInHeader
3. rewrite -- requires: headers in every dependent script (plain and same-package refs; cross-package/tag/symbolic refs untouched)
4. rewrite pgpm.plan textually/format-preservingly via renameInPlanContent (change tokens, [deps], tag lines — timestamps/planners/comments/pkg: refs untouched)

SQL statement bodies are intentionally not touched — schema-name rewrites inside SQL remain the caller's AST-transform concern (transform-schemas), so this primitive composes as parse → rename → transform.

Also:

• deriveRenamesFromSchemaMapping(moduleDir, schemaMapping) — maps a schema rename (e.g. my-app → my_app) to the change renames for every plan change under schemas/<old>/, mirroring what constructive-db's transform-directory.ts does with directory renames + regexes today.
• validateRenames — rejects unknown sources, colliding targets (unless the target is itself renamed away), duplicate targets, self-renames; renameChanges also refuses to overwrite existing files on disk.

Purely additive; no existing code paths changed. 12 new tests; full pgpm/core suite green (402/402). Next step per the plan: refactor constructive-db's transform-directory.ts onto this with a byte-identical generated-output gate.

Note: pnpm lint in pgpm/core fails on main already (ESLint 9 vs .eslintrc config, preexisting, same as noted on #1401).

Link to Devin session: https://app.devin.ai/sessions/ad40d16f38a349b48eb7ce9375e27e6e
Requested by: @pyramation

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