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/specs/go-client/spec.md

@@ -53,6 +53,9 @@ The client SHALL provide a `kb search <query>` command that sends the query to t
 #### Scenario: Human-readable search output
 - **WHEN** the user runs `kb search "how to change oil"`
 - **THEN** the client SHALL POST to `/api/v1/search`, and display results in a human-readable format showing rank, score, document title, page/section, doc type, tags, and a text snippet
+- **THEN** the client SHALL parse search results as flat objects with top-level `title`, `doc_type`, `tags`, `score`, `text`, `chunk_index` fields
+- **THEN** the client SHALL extract `page` from `chunk_metadata` when present (PDF documents)
+- **THEN** the client SHALL extract `section_header` from `chunk_metadata` when present (markdown documents)
 
 #### Scenario: JSON search output
 - **WHEN** the user runs `kb search "query" --format json`
@@ -66,6 +69,22 @@ The client SHALL provide a `kb search <query>` command that sends the query to t
 - **WHEN** the user runs `kb search "error" --fts-only`
 - **THEN** the client SHALL set `fts_only: true` in the request body
 
+#### Scenario: PDF result with page number
+- **WHEN** a search result has `chunk_metadata` containing `{"page": 12}`
+- **THEN** the human output SHALL display "Page 12" in the location line
+
+#### Scenario: Markdown result with section header
+- **WHEN** a search result has `chunk_metadata` containing `{"section_header": "Installation > Prerequisites"}`
+- **THEN** the human output SHALL display "Installation > Prerequisites" in the location line
+
+#### Scenario: Result with both page and section
+- **WHEN** a search result has `chunk_metadata` containing both `page` and `section_header`
+- **THEN** the human output SHALL display both separated by " / "
+
+#### Scenario: Result with no location metadata
+- **WHEN** a search result has empty `chunk_metadata` or no page/section keys
+- **THEN** the human output SHALL omit the location line entirely
+
 ---
 
 ### Requirement: Add note command