feat(tiptap): extend SuggestionReviewPopover to non-rich-text fields (text, textarea, select, etc.)

[suleimansh]

Context

`SuggestionReviewPopover` (#249) currently lives inside `TiptapEditor` only. When an AI suggestion targets a plain TextField, TextareaField, SelectField, or similar non-rich-text field, there is no equivalent step-through popover.

Goal

One popover for all fields. When a pending suggestion arrives for any field type, the popover should appear anchored to that field's DOM element and walk the user through Accept / Reject.

Acceptance criteria

• A shared `SuggestionReviewPopover` is mounted at the page/panel level (not inside each field)
• It subscribes to the global `PendingSuggestionsContext` queue
• For RichText fields: existing inline-diff region stepping (current behaviour)
• For plain fields (text, textarea, select, etc.): shows current value (red/struck) vs. suggested value (green)
• Accepting applies the value to the field (via the suggestion bridge)
• Popover anchors to the field root DOM element
• Skip (dismiss without deciding) is supported; Back navigates to a previous suggestion

Notes

• `SuggestionBanner` is dropped from `TiptapEditor` as of Tiptap diff: single floating popover wizard for per-suggestion approve/reject #249; the global banner (separate issue) replaces it
• Build on `usePendingSuggestionsForField` + `usePendingSuggestions`