feat(review): render 'view diff' anchor links per file in the changed-files summary

[JSONbored]

Enhance the changed-files summary table rows with a GitHub Files-changed anchor link per file/group so maintainers jump straight to the diff. Small render enhancement on top of the summary-table slice; deterministic, no AI.

Deliverables

• Build the per-file ../files anchor (GitHub PR Files tab #diff- style) in the summary-table renderer
• Only for per-file rows (not collapsed group rows); omit when path can't be anchored
• Public-safe URL construction (repo full name + PR number already in context)
• Tests: per-file row link, collapsed group → no link (both branches)

References

• src/review/unified-comment.ts:505
• part of #1957

Part of #1957.

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size: XS · held for later release (gittensor:bug once activated)

[linear-code]

JSO-2258