fix(ui): tool dimming, chronological scrollback, status position

[0xCheetah1]

• Tool calls render in subdued grey text with increased indent so assistant responses visually dominate the scrollback.
• Tools and assistant text share a single chronological scrollback array instead of rendering in separate immutable regions, keeping tool results inline with the text that led to them.
• Streamed text is committed to the scrollback before a tool starts so the assistant's words appear above the tool they precede.
• Status messages now render directly above the input box instead of at the top of the UI.
• A waiting spinner appears between the last tool completion and the next model response, removing dead air.
• Active running tools remain visible during permission prompts so the user can see what needs approval.