What is in this PR

• Renames user-facing "formula" terminology to "expression" in the Page Builder, Automation, and related integration components, in line with the terminology split proposed in docs/decisions/005-formulas-vs-expressions-terminology.md
• Updates locale strings in builder/locales/en.json and integrations/locales/en.json (e.g. getFormulaComponent → getExpressionComponent, etc.
• Updates JSDoc comments in ApplicationBuilderFormulaInput.vue to use "expression"
• Adds the decision document explaining the rationale for the split

How to test this PR

• Click around WAB (there aren't made references to formula) and see it renamed to expression.

Checklist

• A changelog entry has been added to changelog/entries/unreleased using changelog/src/changelog.py
• New/updated Premium/Enterprise features are separated correctly in the premium or enterprise folder
• The latest Chrome and Firefox have been used to test any new frontend features
• Documentation has been updated
• Quality Standards are met
• Performance: tables are still fast with 100k+ rows, 100+ field tables
• The redoc API pages have been updated for any REST API changes
• Our custom API docs are updated for changes to endpoints accessed via API tokens
• The UI/UX has been updated following the UI Style Guide
• Security impact of change has been considered