fix: add reaction display to inline review comments on diff tab

[AbhiVarde]

Fixes #345
Also fixes #347

Reactions were working on the Conversation tab but not on the Code (diff) tab.
The Code tab renders inline review comments inside SingleFileDiff → InlineCommentDisplay in pr-diff-viewer.tsx, but had no reaction UI wired up.

Changes in apps/web/src/components/pr/pr-diff-viewer.tsx:

• Imported ReactionDisplay and Reactions type from @/components/shared/reaction-display
• Added reactions field to the ReviewComment interface
• Rendered <ReactionDisplay> below each inline comment body, using contentType="pullRequestReviewComment"

Changes in apps/web/src/components/shared/reaction-display.tsx:

• Deduplicated users in getUsersForReaction to prevent duplicate avatars and React key warnings
• Added duplicate guard in optimistic update when adding a reaction

Screenshots

Before

After

[vercel]

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