fix(vscode): respect Git diff collapse attributes

[marius-kilocode]

What Problem This Solves

The diff viewer did not apply repository linguist-generated preferences from .gitattributes, so generated translation files opened expanded by default.

Why This Change Was Made

Read Git attributes for every diff source, preserve explicit generated and visible rules, use index attributes for staged diffs, and keep classification changes coherent with local detail caching. Generated files remain manually expandable, while explicitly visible files such as English and German translations open by default.

User Impact

Generated files configured by the repository stay collapsed in workspace, staged, unstaged, session, turn, and Agent Manager diffs. The existing expand-all behavior remains available.

Evidence

• bun run typecheck
• bun run compile
• bun run lint
• bun run test:unit (4,993 passed, 1 skipped)
• Focused diff tests passed

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (16 files)

• .changeset/git-diff-attributes.md
• packages/kilo-vscode/src/agent-manager/local-diff-cache.ts
• packages/kilo-vscode/src/agent-manager/local-diff.ts
• packages/kilo-vscode/src/diff/shared/git-attributes.ts
• packages/kilo-vscode/src/diff/sources/catalog.ts
• packages/kilo-vscode/src/diff/sources/git-status.ts
• packages/kilo-vscode/src/diff/sources/session.ts
• packages/kilo-vscode/src/diff/sources/staged.ts
• packages/kilo-vscode/src/diff/sources/turn.ts
• packages/kilo-vscode/src/diff/sources/unstaged.ts
• packages/kilo-vscode/tests/unit/agent-manager-diff-state.test.ts
• packages/kilo-vscode/tests/unit/diff-session-source.test.ts
• packages/kilo-vscode/tests/unit/diff-turn-source.test.ts
• packages/kilo-vscode/tests/unit/local-diff.test.ts
• packages/kilo-vscode/webview-ui/diff-viewer/diff-open-policy.ts
• script/kilocode-duplication-allowlist.json

---

_{Reviewed by grok-4.6 · Input: 262K · Output: 25.6K · Cached: 997.2K}

_{Review guidance: REVIEW.md from base branch main}