feat: global suggestion banner showing total changes count across all fields

[suleimansh]

Context

The per-field `SuggestionBanner` accordion is being dropped (#249) in favour of the `SuggestionReviewPopover`. A single global banner should replace it, sitting at the page/form level and tracking the overall review progress.

Design

• One banner per form/page (not per field)
• Shows total pending suggestions count + done count: e.g. "3 changes suggested · 1/3 reviewed"
• Sparkle icon, minimal chrome — no accordion, no per-field grouping
• "Accept all" / "Reject all" bulk controls
• Updates in real time as the user steps through via the popover

Acceptance criteria

• Global banner component that reads from `PendingSuggestionsContext`
• Displays aggregate counts across all fields in the current form
• Bulk Accept all / Reject all triggers all pending suggestions
• Disappears when all suggestions are resolved
• Works alongside the per-field popover (they don't conflict)