[FEATURE]: TUI: Separate pane for model thoughts/progress output

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Feature request

Currently, model thinking/reasoning is displayed inline in the conversation (toggled via /thinking), with a flashing blue progress bar while active. This makes conversations harder to follow — thoughts interrupt the message flow and the progress indicator gives no detail about what's happening.

Proposed: Add a dedicated thoughts/progress pane in the TUI, positioned in the right-hand column (below or separate from the existing context/LSP/todo panel). This pane would:

• Display live thinking/reasoning output as it streams, without cluttering the conversation thread
• Replace (or supplement) the blue progress bar with readable, scrollable progress text
• Keep the conversation pane clean — only user messages and final AI responses
• Persist across the session so you can scroll back through reasoning without it being interleaved with replies

Why: The conversation pane is the primary working surface. Mixing reasoning blocks into it degrades readability, especially in long sessions. A dedicated pane treats thoughts as a first-class diagnostic layer without forcing users to choose between "no visibility" (collapsed) and "cluttered conversation" (expanded inline).