[BUG/FEATURE]: Desktop GUI - Thinking process disappears and cannot be viewed in detail #8789

Problem Description

In the Desktop GUI (not TUI), there are two issues with the thinking/reasoning display:

Issue 1: Thinking content disappears after completion

• When using a thinking model (e.g., Claude with extended thinking), the thinking process is visible during streaming
• Once thinking completes, the content disappears from the GUI entirely
• Users cannot review the model's reasoning process after the fact

Issue 2: No detailed thinking view

• Even when manually expanding the thinking block, it does not show the full/detailed thinking content
• The detailed thought chain that was visible during streaming is lost

Expected Behavior

1. Thinking blocks should persist after completion (like in TUI with /thinking toggle)
2. Users should be able to expand thinking blocks to see the full detailed reasoning
3. This setting should be persistable (remember user preference across sessions)

Current Behavior

• Thinking content vanishes after the model finishes reasoning
• No way to review the reasoning process
• No persistent setting to control thinking visibility in Desktop GUI

Environment

• OpenCode Desktop App (latest)
• Affects all thinking-enabled models

Reference

• TUI has /thinking command that works correctly with kv.signal("thinking_visibility", true) persistence
• Desktop GUI lacks equivalent functionality

Suggested Implementation

• Add a toggle in Desktop GUI settings/toolbar to control thinking visibility
• Persist the thinking content in the message history
• Store user preference for default expanded/collapsed state