feat: add visual workflow automation builder

[mpge]

Summary

• Add a complete visual workflow builder UI for creating event-driven automations with 10 trigger types, conditional logic (AND/OR with contextual operators), and 13 action types including delays, webhooks, email notifications, and variable token interpolation
• Three new pages: Workflow list (Index.vue) with drag-to-reorder and active/inactive toggle, visual step-by-step Builder (Builder.vue), and execution Logs page (Logs.vue) with expandable action-by-action detail
• Five new components: WorkflowTriggerSelector, WorkflowConditionBuilder, WorkflowActionList, WorkflowActionConfig, VariableTokenInput
• Full i18n support across all 4 locales (en, fr, de, es) and admin nav integration at position 53

Test plan

• 38 new Vitest tests across 4 test files (all passing)
• WorkflowTriggerSelector: trigger rendering, selection, emission, highlight state
• WorkflowConditionBuilder: AND/OR toggle, add/remove conditions, field-specific operators, preview text
• WorkflowActionList: add/remove/reorder actions, delay rendering, action summaries
• WorkflowBuilder: form rendering, step display, create vs edit mode, form submission
• All 499 existing tests continue to pass
• ESLint clean (no new warnings), Prettier formatted