fix: add pregenerate cleanup to SDK packages to remove stale files

[pyramation]

Summary

Adds pregenerate scripts to each SDK package that clean generated output directories before codegen runs. This prevents stale files from deleted database entities (e.g. uuidModule.ts) from persisting and causing build failures when they reference types that no longer exist.

Companion to constructive-db#595 which applies the same fix to the constructive-db repo.

Changes:

• Added rimraf (^6.1.3) as a root devDependency
• Added pregenerate script to constructive-sdk, constructive-cli, and constructive-react that removes src/{admin,auth,objects,public} and src/index.ts
• Added pregenerate:migrate-client to constructive-sdk that removes ../migrate-client/src/migrate and ../migrate-client/src/index.ts
• Updated all generate scripts to run their pregenerate step first

Review & Testing Checklist for Human

• Verify constructive-cli cleanup list is safe: The CLI has non-generated files in src/ (cli-commands.ts, cli.ts, commands/, config/, utils/) — confirm the pregenerate list only targets generated dirs (admin, auth, objects, public, index.ts) and doesn't touch these
• Verify pregenerate:migrate-client relative path: Runs from sdk/constructive-sdk/ and targets ../migrate-client/src/migrate — confirm this resolves correctly
• Check pnpm-lock.yaml for unintended changes: The lockfile has @types/node version shifts (25.5.0 → 22.19.15) that appear to be pnpm re-resolution noise from adding rimraf — verify these don't cause type issues
• End-to-end test: Run the full generation pipeline after merging and confirm stale files are properly cleaned and builds pass

Notes

• The cleanup lists are hardcoded — if new codegen targets are added in the future, the pregenerate scripts will need updating to include them.
• This does not modify the codegen library itself (@constructive-io/graphql-codegen); the cleanup is at the script level.

Link to Devin session: https://app.devin.ai/sessions/08781f0838fd4c929bb5ab08052b2b5a
Requested by: @pyramation

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