Standardize action button icons and classify CTA hierarchy

[inderdeepsinghgill]

Summary

This PR improves button consistency across the frontend by standardizing icon usage for high-signal actions (create, save, delete) and refining CTA hierarchy on Classify.

What Changed

• Added leading plus icons to create/add actions in Tables, Rows, Columns, Lookups, Groups, and Classify.
• Added save and delete icons in Table Settings actions.
• Added trash icons to destructive confirmation actions (Tables, Documents, Group Detail).
• Updated Classify "Create new model" CTA hierarchy:
  • Uses primary style when no models exist (empty state intent).
  • Uses secondary/outline style when models already exist.

Why

• Improve scanability and action recognition for common operations.
• Reduce visual inconsistency between similar actions across pages.
• Align CTA prominence with user intent by state (empty vs populated).

Out of Scope (Intentional)

• No changes to duplicate empty-state/header CTA patterns.
• No ActionIcon abstraction migration (Mantine ActionIcon -> shared UI wrapper).

Validation

• npm -w apps/frontend run type-check
• npm -w apps/frontend run lint
  • Lint reports only pre-existing warnings outside this change set:
    • apps/frontend/src/App.css
    • apps/frontend/src/ui/bcds-upload-panel.css

QA Guide

• Tables:
  • Verify icons appear for Create Table, Create Row, Add Column, Add Lookup.
  • Verify Save Settings and Delete Table include icons.
  • Verify destructive confirmations include trash icons.
• Groups:
  • Verify Create Group includes plus icon.
  • Verify Delete Group confirm action includes trash icon.
• Classify:
  • With no models, "Create new model" appears as primary.
  • With existing models, "Create new model" appears as secondary.
• Documents:
  • Verify delete confirmation action includes trash icon.

Risk

Low. Changes are UI-only and localized to button props/icons; no API contracts or data models changed.

[inderdeepsinghgill]

Closing as duplicate. Continuing all work and review on #206 (same head branch).