v0.20.0: thinking blocks, chat windows overhaul, scroll fix

Backend:
- Add isThinking flag to agentEvent for text before tool calls
- Separate thinking from response text in runChatTurn and continue.go
- Persist thinking in a dedicated field in message content

Frontend:
- Add thinking field to MessageContent, ChatMessage, ChatTextEvent types
- Create ThinkingBlock.svelte — collapsible block with brain icon
- SSE handler moves text_delta content to thinking on isThinking flag
- Render thinking block between tools and response in ChatThread
- Fix chat window scroll reset on focus change (stable windowKeys order)
- Remove redundant #key id wrapper in WindowLayer
- Enlarge sidebar rail (24→32 default, 40→60 max)
- Remove glyph from sidebar, square graph at top
- Replace AgentTrace/ToolCallCard/UnifiedTimeline with TurnTrace/ToolLine

plans/index.md

@@ -66,6 +66,7 @@ See [`done/`](done/) for executed plans:
 | 2026-08-03 | [Nomos chat: reliability & predictability audit](done/2026-08-03-nomos-chat-reliability-and-ux-audit.md) |
 | 2026-08-03 | [Adopt cyberspace.online terminal aesthetic + dithered images](done/2026-08-03-cyberspace-style-adoption.md) |
 | 2026-08-03 | [Nomos chat: working-visibility, message queue, generation-aware timeline](done/2026-08-03-nomos-chat-working-visibility.md) |
+| 2026-08-04 | [Chat interaction overhaul: inline progressive stream + thinking blocks](done/2026-08-04-chat-window-overhaul.md) |
 
 ## Conventions