Fix search human-mode output to match engine API response

The Go client struct expected a nested document object and top-level
page/section fields, but the engine returns flat results with metadata
in chunk_metadata. This caused empty display for title, type, tags,
page, and section in human output mode.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

openspec/changes/archive/2026-04-02-fix-search-human-output/.openspec.yaml

@@ -0,0 +1,2 @@
+schema: spec-driven
+created: 2026-04-02