Add auto-collapse option for large file lists in PR comments

[Copilot]

PR comments with dozens of changed files become unwieldy noise. When more than 20 file rows are present, file rows should collapse into a <details> block while Total and Tarball size rows remain always visible.

Changes

• New auto-collapse input (default: true) — when enabled and file count exceeds 20, file rows are wrapped in a <details><summary>Show files (N files)</summary> block; total rows stay visible above it
• Both report modes updated — regression and head-only templates implement the same collapsing logic
• auto-collapse: false disables the behavior entirely regardless of file count

Usage

- uses: pkg-size/action@v1
  with:
    auto-collapse: false  # disable if you always want the full flat table

---

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[github-actions]

📊 Package size report   0.2%↑

File	Before	After
dist/index.js	760.3 kB	0.1%↑761.3 kB
README.md	9.3 kB	4%↑9.7 kB
Total (Includes all files)	772.3 kB	0.2%↑773.7 kB
Tarball size	203.5 kB	0.2%↑203.9 kB

Unchanged files

File	Size
LICENSE	1.1 kB
package.json	1.6 kB

_{🤖 This report was automatically generated by pkg-size-action}