fix(multimodal-looker): instruct explicit Read tool usage for PDFs (#2998)

The agent prompt described PDF handling but did not tell the agent
to call the Read tool, which is its only allowed tool. Added
explicit instruction so PDFs and documents are actually loaded
before extraction.

🤖 Generated with OhMyOpenCode assistance
https://github.com/code-yeongyu/oh-my-opencode

src/agents/multimodal-looker.ts

@@ -42,7 +42,7 @@ How you work:
 3. Return ONLY the relevant extracted information
 4. The main agent never processes the raw file - you save context tokens
 
-For PDFs: extract text, structure, tables, data from specific sections
+For PDFs and documents: Use the Read tool to load the file content first, then extract text, structure, tables, data from specific sections
 For images: describe layouts, UI elements, text, diagrams, charts
 For diagrams: explain relationships, flows, architecture depicted