feat(pr-management): add interactive review findings pane Claude Code mod (part of #1497) #1887

What should happen

pr-management-code-review should display drafted code review findings in an interactive terminal review pane (ui.render Pane) when running under Claude Code, allowing maintainers to inspect findings and toggle individual inline comments ([Accept] / [Skip] / [Edit]) directly rather than stepping through sequential text prompts.

Why

During deep code review (Step 6 / Step 7a in review-flow.md), reviewing inline comment candidates currently requires text-prompt interactions ([A]ll, [N]one, 1,3, -2, [E 2]). As identified in #1497, moving this presentation to an interactive terminal pane (ui.render) provides a zero-token visual review surface, removes interactive prompt roundtrips, and accelerates review triage while maintaining strict vendor-neutral Markdown fallbacks across other harnesses.

Which layer

Other / unsure

Boundary conditions (optional)

• Vendor Neutrality: When running on non-Claude harnesses (Codex, Antigravity, Cursor, CI) or when mods are disabled/unsupported, the skill must cleanly fall back to the existing Markdown prompt flow in review-flow.md without throwing errors or halting execution.
• Empty Findings: If a review yields zero findings (clean approval), the pane hook must cleanly pass through (next(e)) without rendering empty UI frames.
• Anchor Handling: Findings anchored to file:line should be clearly distinguished from unanchored general observations (which fold into the body's Smaller observations).
• Graceful Fallback: If UI resolution fails or runs in a constrained/narrow terminal, it should fall back cleanly to standard text blocks.

Out of scope (optional)

• Autonomous review submission: maintainers retain full control and must explicitly confirm the final review submission.
• Modifying backend capability tools in tools/pr-management/.
• Replacing agent reasoning: diff analysis, severity classification, and finding generation remain in the skill.

References (optional)

• Part of Explore Claude Code mods across the skill families #1497 (Explore Claude Code mods across the skill families)
• docs/when-to-use-mods.md
• plugins/magpie-pr-management/skills/code-review/review-flow.md