Add editable survey instructions and email subjects

[ttenneb]

Summary

• add persisted, editable survey instructions displayed above respondent surveys
• add localized invitation email subjects alongside existing localized email bodies
• add dashboard editors with dirty-state, save/import, and cross-survey race protections
• preserve legacy instruction, subject, language, and CSV behavior through defaults and normalization
• apply configured subjects to bulk invitations and test/reminder emails

Database

• add additive Liquibase migration v1_5_editable_survey_content.sql
• add and backfill Survey.instructions
• add and backfill EMAIL.subject
• widen EMAIL.text to TEXT without dropping data

Security and compatibility

• enforce existing organization-scoped read/editor role checks
• validate subject length and reject control characters
• return respondent instructions only after respondent-token validation
• canonicalize legacy language codes and quoted labels without destructive migration
• support legacy language_code,notification_text CSV files

Testing

• npm test --prefix api — 39 passed
• npm test --prefix dashboard — 11 passed
• npm run build --prefix dashboard — passed
• npm run build --prefix network-survey — passed
• node --check api/server.js — passed
• git diff --check — passed

Multiple fresh adversarial reviews were completed. All reported blockers were fixed and regression-tested; the final two reviews reported no blockers.