fix(cosh): remove 24-item limit on @ file completion menu

[kongche-jbw]

Description

Remove the hardcoded maxResults cap (MAX_SUGGESTIONS_TO_SHOW * 3 = 24) in useAtCompletion.ts that limited the @ file selection menu to only 24 results. The UI layer already supports scrolling through unlimited results with 8-per-page pagination (▲/▼ indicators, (current/total) counter, wrap-around navigation).

Related Issue

• Related issue linked (recommended for new features and non-trivial changes)

fixes #89

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional change)
• Performance improvement
• CI/CD or build changes

Scope

• cosh (copilot-shell)
• agent-sec-core
• os-skills
• agentsight
• Multiple / Project-wide

Checklist

• I have read the Contributing Guide
• My code follows the project's code style
• I have added tests that prove my fix is effective or that my feature works
• I have updated the documentation accordingly
• For cosh: Lint passes, type check passes, and tests pass
• For agent-sec-core (Rust): cargo clippy -- -D warnings and cargo fmt --check pass
• For agent-sec-core (Python): Ruff format and pytest pass
• For os-skills: Skill directory structure is valid and shell scripts pass syntax check
• Lock files are up to date (package-lock.json / Cargo.lock)

Testing

• Existing useAtCompletion test suite (13 tests) all pass
• npm run build succeeds with no errors
• Verified that removing maxResults lets the backend (fileSearch.ts) return all matching results via its default Infinity behavior

Additional Notes

The root cause was in useAtCompletion.ts:202 where maxResults: MAX_SUGGESTIONS_TO_SHOW * 3 capped search results at 24. Since the UI (useCompletion.ts + SuggestionsDisplay.tsx) already had full scroll/pagination support, simply removing this cap resolves the issue without any display-layer changes.

[kongche-jbw]