## Context

The engine's `/api/v1/search` endpoint returns flat result objects:

```json
{
  "chunk_id": 123,
  "score": 0.031,
  "text": "...",
  "chunk_index": 3,
  "chunk_metadata": {"page": 12, "section_header": "Installation"},
  "title": "Git Admin Guide",
  "doc_type": "pdf",
  "source_path": "/home/user/docs/git-admin.pdf",
  "created_at": "2026-03-15T10:30:00",
  "tags": ["git", "admin"]
}
```

The Go client's human-mode struct in `client/cmd/search.go` incorrectly expects a nested `document` object and top-level `page`/`section` fields. This causes all metadata to display as zero values.

## Goals / Non-Goals

**Goals:**
- Fix the search result struct to match the flat engine response
- Extract `page` and `section_header` from `chunk_metadata` for human display
- Maintain identical JSON output (already passes through raw response)

**Non-Goals:**
- Changing the engine API response format
- Adding new display fields beyond what was originally intended

## Decisions

**Flatten the struct to match API response.** The result struct will have `Title`, `DocType`, `Tags` as top-level fields (matching `title`, `doc_type`, `tags` JSON keys). `ChunkMetadata` will be decoded as `map[string]interface{}` to extract `page` and `section_header` dynamically, since its contents vary by document type.

**Why not a typed ChunkMetadata struct?** The metadata keys depend on the ingestion pipeline (PDFs have `page`, markdown has `section_header`, code may have others in future). A map is more resilient to engine-side additions.

## Risks / Trade-offs

- [Minimal risk] If the engine adds new top-level fields, the Go struct silently ignores them — this is existing behavior and acceptable for human-mode display.