Summary

@pgpmjs/export had become the accidental home of the whole source-agnostic dials pipeline (#1569, #1571, #1572). This splits it back into one-package-per-front-door, with the shared engine glue in @pgpmjs/transform:

@pgpmjs/transform   (engine)      ← + restructure.ts, partition.ts, module-source.ts, catalog-check.ts
@pgpmjs/export      (live DB)     ← keeps introspection/graphql/meta exporters only
@pgpmjs/import  NEW (dumps)       ← dump-source.ts, import.ts (importDumpRows, linkTextualDeps, COPY handling)
@pgpmjs/diff    NEW (semantic diff) ← diff-source.ts (DiffSide, sqlToDiffChanges, deltaChangesToRows)

• transform gains a @pgpmjs/ast dep (PgpmRow, parsePlanFile, readScript) instead of the old @pgpmjs/core imports — core depends on transform, so the moved files now sit below core in the graph. restructureExportRows, partitionExportRows, parsePartitionConfig, loadModuleSource, snapshotCatalog/diffCatalogSnapshots are all re-exported from @pgpmjs/transform.
• @pgpmjs/import and @pgpmjs/diff are pure leaves over ast + naming-spec + transform; export is no longer in their dependency path.
• CLI commands are unchanged behaviorally — commands/{import,diff,transform,export}.ts just import from the new homes; pgpm/cli adds @pgpmjs/import + @pgpmjs/diff deps.
• Tests move with their sources (module-source.test.ts → transform, dump-source/import-rows → import, diff-source → diff). No test logic changed.

Pre-existing (verified identical on clean main): 7 failures in pgpm/export meta-config tests (routing_public vs constructive_routing_public naming) are unrelated to this move.

Refs: constructive-planning#1340, constructive-planning#1329; follows #1569/#1571/#1572.

Link to Devin session: https://app.devin.ai/sessions/98edd75e27db4328aec77c581e211092
Requested by: @pyramation