Redesign PR comments with visual progress bars and status icons

[Affanmir]

Summary

• Redesign PR comment templates following Material Design principles for better visual hierarchy and scannability
• Add Unicode progress bar (████████████████░░░░) showing coverage/quality percentage at a glance
• Add per-file colored status icons: 🟢 (≥90%), 🟡 (≥70%), 🔴 (<70%)
• Replace vague "Meets/Below threshold" wording with clear Passed / Failed status
• Add emoji icons to metrics table rows for quick visual scanning
• Use distinct report headers: 🛡️ for coverage, 🔬 for quality
• Cleaner footer with marketplace link

Before vs After

Before:

## ✅ Diff Coverage: 82.0%
> ✔️ Meets threshold of 80%
| Metric | Value |
| Coverage on diff lines | 82.0% |
| Lines changed | 50 |

After:

### 🛡️  Diff Coverage Report
**82.0%**  `████████████████░░░░`
> ✅  Passed — meets threshold of 80%
| 📏 | Lines in diff | 50 |
| 🔍 | Lines uncovered | 9 |
| 📁 | Files changed | 3 |

Files Changed

• src/comment.py — Added _progress_bar() and _status_icon() Jinja2 filters
• src/outputs.py — Same filters for step summary rendering
• templates/comment_coverage.md.j2 — Redesigned coverage PR comment
• templates/comment_quality.md.j2 — Redesigned quality PR comment
• templates/step_summary.md.j2 — Redesigned step summary
• tests/test_comment.py — Updated assertions for new wording
• README.md — Updated comment previews to match new design

Test plan

• All 75 tests pass
• Ruff lint clean
• Ruff format clean
• Verify PR comment renders correctly on a real PR
• Verify step summary renders correctly in Actions UI

🤖 Generated with Claude Code

[github-actions]

████████████████████ 100.0% on changed lines

0 lines changed   0 uncovered   0 files

 📋 Full diff-cover report

Diff Coverage

Diff: origin/main...HEAD, staged and unstaged changes

No lines with coverage information in this diff.

_{🛡️ diff-cover-action}