feat(pgpm): pgpm regen — generate revert/verify scripts from deploys

[pyramation]

Summary

Adds pgpm regen (constructive-io/constructive-planning#1329 dials roadmap; distinct from the future pgpm generate, constructive-io/constructive-planning#1333): fills in a module's revert/ and verify/ scripts mechanically from its deploy/ scripts, using the same @pgsql/scripts substrate that #1562 wired into restructured exports (classifyStatements → revertFor/verifyFor).

pgpm regen                      # sweep: every plan change whose revert/verify is missing or an empty stub
pgpm regen <change...>          # targeted mode
    --revert-only|--verify-only
    --dry-run                   # report what would be written + warnings, write nothing
    --force                     # overwrite non-empty scripts (never done otherwise)

@pgpmjs/transform — new regen module (pure, parser-level):

• classifyScript(sql) — classifyStatements minus TransactionStmt (the BEGIN/COMMIT wrapper scripts carry is the file convention's job, not a statement to invert)
• isStubScript(sql) — stub = parses to zero substantive statements (comments, whitespace, bare transaction wrapper). Unparseable content is not a stub, so it is never overwritten.
• regenerateScripts(deploySql) → { revert, verify } (GeneratedScripts with warnings)

pgpm CLI — commands/regen.ts (engine-exempt, no DB connection): iterates pgpm.plan, reads deploy/<change>.sql, and writes generated scripts in repo convention — -- Revert <change> from pg + BEGIN;…COMMIT;, -- Verify <change> on pg + BEGIN;…ROLLBACK;. Non-derivable statements (e.g. DML) become -- revert not derivable: <reason> comments; the run ends with a generated / skipped / warnings summary.

Tests

• pgpm/transform/__tests__/regen.test.ts — stub detection, wrapper exclusion, revert ordering, verify checks, non-derivable warnings
• pgpm/cli/__tests__/regen.test.ts — sweep/targeted, --force, --dry-run, --revert-only/--verify-only, file emission conventions
• pgpm/cli/__tests__/regen-e2e.test.ts — fixture module with mixed kinds (schema, table, ALTER columns/constraints, function, trigger, RLS policy, grant, index), all stubs → pgpm regen → live-Postgres round-trip: deploy → pgpm verify passes → pgpm revert leaves the DB clean (schema gone, ledger empty)

pnpm-lock.yaml re-resolved by pnpm 10 for the new @pgpmjs/transform dep of pgpm (same wholesale normalization as #1562).

Link to Devin session: https://app.devin.ai/sessions/d84ba7255ddc405ea0f83f21b3247642
Requested by: @pyramation

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