Update pivot and flat view toggle buttons

[ericokuma]

Replaces the single "Pivot/Flat table" toggle button with a dual-mode FieldSwitcher component in the Pivot Toolbar. This addresses APP-348 by providing a clearer, more discoverable way for users to switch between Pivot and Flat views, always showing both options and indicating the active mode.

Closes APP-348

Checklist:

• [ ] Covered by tests
• [x] Ran it and it works as intended
• [x] Reviewed the diff before requesting a review
• [x] Checked for unhandled edge cases
• [x] Linked the issues it closes
• [ ] Checked if the docs need to be updated. If so, create a separate Linear DOCS issue
• [ ] Intend to cherry-pick into the release branch
• [ ] I'm proud of this work!

---

Linear Issue: APP-348

[cursor[bot]]

Cursor Agent can help with this pull request. Just @cursor in comments and I'll start working on changes in this branch. _{Learn more about Cursor Agents}