[Feature]: Suggestion review with diff view and bulk actions

[bjrump]

Problem Statement

The Suggestions Section renders each Suggestion as plain text with only single Apply/Dismiss buttons (apps/frontend/components/settings/sections/SuggestionsSection.tsx). Reviewers cannot see what actually changes (no before/after), and reviewing many Suggestions is one-at-a-time.

Proposed Solution

• Diff view: show the original source description / entity vs. the proposed text, with change highlighting. For a Source Correction show old → new; for an Entity Addition show the new fact in context.
• Bulk actions: per-row selection checkboxes plus "Apply selected" / "Dismiss selected".

Apply/Dismiss logic already exists (applyProjectSuggestion, deleteProjectSuggestion in apps/frontend/lib/api); this is primarily a review-UX enhancement. Bulk apply iterates existing mutations (or a small batch endpoint if needed).

Acceptance Criteria

• Each Suggestion shows a before/after comparison appropriate to its kind (Source Correction / Entity Addition).
• Multiple Suggestions can be selected and applied or dismissed together.
• Apply remains irreversible and keeps its existing warning; Dismiss removes permanently (per domain rules).
• de + en strings.

Scope / Notes

Frontend (mostly); a batch endpoint in apps/api is optional. Personal (user-owned) Projects have no Suggestion management — keep that exclusion.