feat(ui): increase terminal scrollback buffer and document client-side config

docs/API.md

@@ -1,5 +1,7 @@
 # myworktree — HTTP API
 
+> **Note**: This document covers the HTTP API. Terminal-related client-side settings (e.g., scrollback buffer size, font size, theme) are handled by the Web UI and are not part of the backend API.
+
 Base URL: printed when starting `myworktree` or `mw`, e.g. `http://127.0.0.1:50053/`.
 `mw` opens the browser automatically by default; `myworktree` prints the URL unless you pass `-open=true`.
 

docs/ARCHITECTURE.md

@@ -41,6 +41,7 @@ It does **not** analyze project code or prevent concurrent write conflicts insid
   - **Handshake Protocol**: Server sends `{"type":"ready"}` on connect; client must wait for this before sending resize to start data flow.
   - **Timeout Handling**: Client should implement 5s handshake timeout with SSE fallback.
   - **Resize Support**: Client sends `{"type":"resize","cols":80,"rows":24}` to update PTY size, triggering TUI programs to redraw.
+  - **Client-side Config**: Terminal buffer size (scrollback) is configurable on the client side to control how much history is retained in memory for scrolling. This is a client-side setting and does not affect server-side log persistence.
 - Fallback path remains available: HTTP input `POST /api/instances/input` + replay/SSE logs (`GET /api/instances/log`, `GET /api/instances/log/stream`).
 - UI shows transport state (`websocket/sse/polling`) and supports manual WS reconnect.
 - Backlog is stored on disk with a size cap (rolling truncate).

docs/PRD.md

@@ -51,6 +51,7 @@
   - WebSocket 握手协议：服务端发送 `{"type":"ready"}`，客户端等待后发送 resize 开始数据流。
   - 窗口尺寸传递：前端监听窗口 resize 并通知后端 PTY，确保 TUI 程序正确重绘。
   - 超时降级：5 秒握手超时后自动降级到 SSE 方案。
+  - 终端配置：Web TTY 的缓冲区（scrollback）、主题、字体等参数由前端灵活配置，以适应不同的调试和使用场景。
 - 规划增强：无（PTY + Web TTY 已完成）。
 
 ## 8. 验收标准（MVP）

internal/ui/static/index.html

@@ -959,7 +959,8 @@ <h3>Start Instance</h3>
             term = new Terminal({
                 convertEol: true, cursorBlink: true,
                 fontFamily: "ui-monospace, SFMono-Regular, Menlo, monospace",
-                fontSize: 13, theme: { background: "#0b1020" }
+                fontSize: 13, theme: { background: "#0b1020" },
+                scrollback: 10000
             });
 
             if (window.FitAddon) {