feat: show ±0 badge when vote median matches official grade

[river0525]

Summary

• getRelativeEvaluationLabel(0) が '' を返していたのを '±0' に変更し、diff=0 でもバッジが表示されるようにした
• getRelativeEvaluationBadgeColorClass(0) にグリーン (bg-green-400/500) を追加
• getRelativeEvaluationTooltipText('±0') に「ユーザは「ふつう」と評価」を追加
• getRelativeEvaluationColorClass(0) を gray → green に統一
• RelativeEvaluationBadge.svelte は変更なし（{#if label} が '±0' を truthy として扱うため）
• seed.ts にデモデータ追加（APG4bPython_co, Q8）

Test plan

• pnpm test:unit src/features/votes/utils/relative_evaluation.test.ts — 38 tests passed
• diff=0 タスクで ±0 バッジが右上に表示されることを目視確認済み
• ツールチップに「ユーザは「ふつう」と評価」が表示されることを確認済み
• E2E テストで既存の投票フローにリグレッションがないことを確認

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features

  • 投票中央値と運営グレードが一致する場合に、右上へ緑色の「±0」バッジを表示する視覚指標を追加。

• Documentation

  • 実装計画と設計仕様を追加し、表示・ツールチップ・アクセシビリティ挙動を明記。

• Tests

  • ±0 ケースのラベル・色・ツールチップ期待値を単体テストで追加・更新。

• Chores

  • デモ用の投票統計データをシードに追加。

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

Plan: Pro

Run ID: 4e0ef168-d2ef-409b-9393-151d23fb2f06

📥 Commits

Reviewing files that changed from the base of the PR and between f564293 and 5e57a70.

📒 Files selected for processing (2)

• docs/superpowers/plans/2026-05-20-zero-diff-badge.md
• docs/superpowers/specs/2026-05-20-zero-diff-badge-design.md

---

📝 Walkthrough

Walkthrough

diff=0（投票中央値と運営グレード一致）のときに ±0 バッジを表示する機能を完成。仕様→実装→テスト→デモデータまで統合的に実装。色表現を gray から green に変更し、ラベル表示を空文字から ±0 へ更新。

Changes

Zero-Diff Badge Implementation

Layer / File(s)	Summary
Design Specification docs/superpowers/specs/2026-05-20-zero-diff-badge-design.md	diff=0 時の ±0 バッジ表示仕様を定義。ラベル、色、ツールチップ、影響範囲（バッジ表示箇所4件）、テスト方針を一式記載。
Implementation Plan and Lessons docs/superpowers/plans/2026-05-20-zero-diff-badge.md	実装計画をタスク形式で整理。対象ファイル、テスト更新手順、追加変更を列挙。Docker 環境の pnpm シンボリックリンク欠損問題と TSDoc 陳腐化に関する教訓を記載。
Core Utility Functions src/features/votes/utils/relative_evaluation.ts	getRelativeEvaluationLabel を diff=0 時に ±0 返却へ変更。getRelativeEvaluationTooltipText に ±0 ケース追加（「ふつう」説明）。getRelativeEvaluationColorClass と getRelativeEvaluationBadgeColorClass の diff=0 時の色を gray→green に、バッジを空文字→green 返却へ更新。
Unit Tests src/features/votes/utils/relative_evaluation.test.ts	相対評価ユーティリティの期待値を更新。ラベル ('' → ±0)、ツールチップ (±0 → ふつう説明)、色クラス (gray → green)、バッジ (空文字 → green) の新規・変更テスト。
Demo Data Seeding prisma/seed.ts	VOTE_STATS_DEMO_DATA と addVoteStatisticsDemoData() を追加。prisma.votedGradeStatistics.upsert で taskId 単位のデモレコード登録。main() で addAnswers() 後に呼び出し。

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Possibly related PRs

• AtCoder-NoviSteps/AtCoderNoviSteps#3416: 相対評価投票機能の初期実装。本 PR の ±0 バッジ機能は同機能の拡張.
• AtCoder-NoviSteps/AtCoderNoviSteps#3447: 相対評価ユーティリティとバッジレンダリングの修正が重なる PR。

Suggested reviewers

• KATO-Hiro

Poem

グレーは緑に変わりて輝く 🟢
差なしの場所に ±0 の印
仕様、実装、テスト、データ並べて
中立がひとつ、声をあげる
小さな改良、大きな整合性

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 54.55% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	Pull request title clearly summarizes the main change: displaying a ±0 badge when vote median matches official grade, which is the primary objective across all modified files.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feature/zero-diff-badge

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Caution

Some comments are outside the diff and can’t be posted inline due to platform limitations.

⚠️ Outside diff range comments (2)

docs/superpowers/plans/2026-05-20-zero-diff-badge.md (1)

1-79: ⚠️ Potential issue | 🟡 Minor | ⚡ Quick win

フォーマット修正が必要です。

• Prettier チェック警告（パイプライン検出）
• コードブロック前後に空行が必要（MD031、lines 66-69）

修正手順：

# Prettier でフォーマット
pnpm format:write docs/superpowers/plans/2026-05-20-zero-diff-badge.md

Line 65 と 70 にも空行を追加してください（MD031 対応）。

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@docs/superpowers/plans/2026-05-20-zero-diff-badge.md` around lines 1 - 79,
The markdown has Prettier/MD031 formatting issues around the shell code block
under the "Docker node_modules シンボリックリンク欠損問題" section beneath the "# ±0
相対評価バッジ表示 Implementation Plan" heading; fix by adding an empty line before and
after the fenced shell code block (the ```shell ... ``` block) and then run the
formatter command pnpm format:write to reformat the file so Prettier passes.

docs/superpowers/specs/2026-05-20-zero-diff-badge-design.md (1)

1-58: ⚠️ Potential issue | 🟡 Minor | ⚡ Quick win

Prettier フォーマット修正が必要です。

パイプラインで Prettier チェックが警告を出しています。

以下を実行してフォーマットを修正してください：

pnpm format:write docs/superpowers/specs/2026-05-20-zero-diff-badge-design.md

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@docs/superpowers/specs/2026-05-20-zero-diff-badge-design.md` around lines 1 -
58, Run the project's Prettier formatter to fix formatting in the markdown spec
titled "# ±0 相対評価バッジ表示機能 — 設計仕様" by executing the formatter command (pnpm
format:write), then stage and commit the changes so the pipeline Prettier check
passes; ensure your local Prettier configuration is used and re-run the CI
check.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Outside diff comments:
In `@docs/superpowers/plans/2026-05-20-zero-diff-badge.md`:
- Around line 1-79: The markdown has Prettier/MD031 formatting issues around the
shell code block under the "Docker node_modules シンボリックリンク欠損問題" section beneath
the "# ±0 相対評価バッジ表示 Implementation Plan" heading; fix by adding an empty line
before and after the fenced shell code block (the ```shell ... ``` block) and
then run the formatter command pnpm format:write to reformat the file so
Prettier passes.

In `@docs/superpowers/specs/2026-05-20-zero-diff-badge-design.md`:
- Around line 1-58: Run the project's Prettier formatter to fix formatting in
the markdown spec titled "# ±0 相対評価バッジ表示機能 — 設計仕様" by executing the formatter
command (pnpm format:write), then stage and commit the changes so the pipeline
Prettier check passes; ensure your local Prettier configuration is used and
re-run the CI check.

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

Plan: Pro

Run ID: d0dd1f9a-2d18-47d3-b07b-53e056b52bc7

📥 Commits

Reviewing files that changed from the base of the PR and between e7133bc and f564293.

📒 Files selected for processing (5)

• docs/superpowers/plans/2026-05-20-zero-diff-badge.md
• docs/superpowers/specs/2026-05-20-zero-diff-badge-design.md
• prisma/seed.ts
• src/features/votes/utils/relative_evaluation.test.ts
• src/features/votes/utils/relative_evaluation.ts