feat: Add .gitignore awareness for file operations

[CarGDev]

Summary

Respect .gitignore patterns when listing files, loading context, and showing file picker.

Why It's Needed

• Context Quality: Don't waste tokens on node_modules, build artifacts
• File Picker UX: Don't show irrelevant files in @ picker
• Search Quality: Grep/glob results exclude ignored files
• Performance: Skip large ignored directories

Current Problem

@ file picker shows:
├── node_modules/           # 50,000+ files
├── dist/                   # Build artifacts
├── .git/                   # Git internals
├── coverage/               # Test coverage
└── src/                    # Actual source

Proposed Behavior

@ file picker shows:
└── src/                    # Only relevant files
    ├── index.ts
    ├── services/
    └── utils/

Implementation

import ignore from "ignore"

async function loadIgnorePatterns(cwd: string): Promise<Ignore> {
  const ig = ignore()
  
  // Load .gitignore
  const gitignore = await readFile(path.join(cwd, ".gitignore"), "utf-8").catch(() => "")
  ig.add(gitignore)
  
  // Load .codetyperignore (custom ignore)
  const codetyperignore = await readFile(path.join(cwd, ".codetyperignore"), "utf-8").catch(() => "")
  ig.add(codetyperignore)
  
  // Always ignore these
  ig.add([
    "node_modules",
    ".git",
    "dist",
    "build",
    "coverage",
    ".codetyper-backup",
  ])
  
  return ig
}

function filterFiles(files: string[], ig: Ignore): string[] {
  return files.filter(f => !ig.ignores(f))
}

Apply To

• File picker (@ mentions)
• Glob tool results
• Grep tool results
• Context file loading
• Directory listings

Configuration

{
  "ignore": {
    "useGitignore": true,
    "useCodyterignore": true,
    "additional": ["*.log", "tmp/"]
  }
}

Acceptance Criteria

• Parse and respect .gitignore
• Support .codetyperignore for custom patterns
• Filter file picker results
• Filter glob results
• Filter grep results
• Always ignore node_modules, .git, dist, build
• Configurable additional ignore patterns

Effort Estimate

0.5 days