fix(terminal): refactor WebSocket cleanup, buffer management, and disposal

- Add proper disposal tracking to prevent memory leaks
- Move terminal buffer from localStorage to sessionStorage
- Restore buffer immediately after first WS message
- Fix clear detection logic and error handling
- Add signal parameter support for abortable fetch requests

💘 Generated with Crush

Assisted-by: MiniMax-M2.7 via Crush <crush@charm.land>

web/src/api/client.js

@@ -105,7 +105,7 @@ const api = {
       }).catch(reject)
     })
   },
-  sendShellChat: (message, context = {}, stream = true, onChunk) => {
+  sendShellChat: (message, context = {}, stream = true, onChunk, signal) => {
     const payload = {
       message,
       cwd: context.cwd || '',
@@ -120,6 +120,7 @@ const api = {
         method: 'POST',
         headers: { 'Content-Type': 'application/json' },
         body: JSON.stringify(payload),
+        signal,
       }).then(async (res) => {
         if (!res.ok) {
           const err = await res.json().catch(() => ({ error: res.statusText }))