feat: --summary mode for token-efficient search output

[ktappdev]

Problem

Current --json output includes full match breakdowns per result:

[
  {
    "path": "src/auth.go",
    "type": "file",
    "score": 85,
    "matches": ["basename:auth", "path:auth", "syn:authentication", "sym:AuthMiddleware"],
    "breakdown": ["basename contains +7", "path contains +4", "..."]
  }
]

For LLM agent consumption, this is hundreds of tokens per query when just paths and scores would suffice for most use cases. --dir-summary already exists for directory-level summaries but nothing for file-level.

Proposed Solution

Add --summary flag that outputs minimal JSON:

[
  {"path": "src/auth.go", "type": "file", "score": 85},
  {"path": "src/login.go", "type": "file", "score": 62}
]

No matches, no breakdown. Just path, type, score.

Implementation Notes

• New --summary flag in command_search.go
• When --summary && --json, strip matches and breakdown from output
• Could also work with non-JSON output: just paths and scores, one per line
• --summary and --dir-summary are orthogonal (both could be true)
• --summary and --explain conflict — error or --explain wins

Acceptance Criteria

• --summary --json outputs [{path, type, score}] only
• --summary without --json outputs compact text format
• --summary and --explain together produce an error or --explain wins
• Token count reduced by ~60-80% compared to full output