feat: add look_at tool and multimodal-looker agent

Add a new tool and agent for analyzing media files (PDFs, images, diagrams)
that require visual interpretation beyond raw text.

- Add `multimodal-looker` agent using Gemini 2.5 Flash model
- Add `look_at` tool that spawns multimodal-looker sessions
- Restrict multimodal-looker from calling task/call_omo_agent/look_at tools

Inspired by Sourcegraph Ampcode's look_at tool design.

🤖 GENERATED WITH ASSISTANCE OF [OhMyOpenCode](https://github.com/code-yeongyu/oh-my-opencode)

src/tools/look-at/constants.ts

@@ -0,0 +1,23 @@
+export const MULTIMODAL_LOOKER_AGENT = "multimodal-looker" as const
+
+export const LOOK_AT_DESCRIPTION = `Analyze media files (PDFs, images, diagrams) that require visual interpretation.
+
+Use this tool to extract specific information from files that cannot be processed as plain text:
+- PDF documents: extract text, tables, structure, specific sections
+- Images: describe layouts, UI elements, text content, diagrams
+- Charts/Graphs: explain data, trends, relationships
+- Screenshots: identify UI components, text, visual elements
+- Architecture diagrams: explain flows, connections, components
+
+Parameters:
+- file_path: Absolute path to the file to analyze
+- goal: What specific information to extract (be specific for better results)
+
+Examples:
+- "Extract all API endpoints from this OpenAPI spec PDF"
+- "Describe the UI layout and components in this screenshot"
+- "Explain the data flow in this architecture diagram"
+- "List all table data from page 3 of this PDF"
+
+This tool uses a separate context window with Gemini 2.5 Flash for multimodal analysis,
+saving tokens in the main conversation while providing accurate visual interpretation.`