Destination tab: move Regenerate to Blueprint box, add toast feedback

[deanleigh]

Problem

The Destination tab has several UX issues:

1. No feedback on Regenerate — The "Regenerate" buttons on Fields and Blocks info boxes are functional but give no visible feedback (no toast, no loading indicator). Users can't tell if anything happened.

2. Two buttons, one action — Both Fields and Blocks Regenerate buttons call the same regenerateDestination() endpoint. Two buttons implies granular control that doesn't exist.

3. Conceptual mismatch — The operation is "re-read the blueprint and rebuild destination.json". A "Re-extract" button on the Blueprint info box would be the natural place — the blueprint is the source of truth for both fields and blocks.

Proposed Changes

• Blueprint box: Add a "Re-extract" button (primary/blue, uSync-style) alongside the existing "Change" button
• Fields/Blocks boxes: Remove Regenerate buttons, keep as read-only summary cards (count + label)
• Toast feedback: Show notification on re-extract with result ("3 fields, 6 blocks" or "unchanged")
• Improved response: Backend returns before/after counts so the toast can show what changed

Planning

See planning/DESTINATION_TAB_REDESIGN.md for full design and sprint breakdown.