feat: add Workable ATS integration

[tybrooks123]

Summary

• adds Workable as an ATS integration with token auth and account URL normalization
• wires Workable into ATS proxy plus jobs, candidates, and departments read/list endpoints
• adds Prisma enum/migration, metadata, seed/field mappings, and Workable preprocessing support

Refs #551

Verification

• git diff --check
• PGSQL_URL=postgresql://user:password@localhost:5432/revert corepack yarn workspace @revertdotdev/backend prisma validate
• corepack yarn workspace @revertdotdev/backend exec tsc --noEmit --skipLibCheck --module NodeNext --moduleResolution NodeNext --target ES2018 --lib ESNext,DOM services/ats/workable.ts routes/v1/ats/authHandlers/workable.ts helpers/crm/transform/preprocess.ts helpers/crm/transform/disunify.ts prisma/client.ts constants/common.ts

Note: full backend build could not run in this checkout because Fern-generated files are missing and fern generate requires login.

[github-actions]

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