Fixes for run_shell.py, chat draft persistency, and BytePlus silent failure

[makiroll1125]

What

• Fix run_shell on Windows so commands with quoted arguments (e.g. claude -p "some prompt") run correctly instead of silently breaking
• Save chat drafts so they don't disappear when switching tabs and coming back
• Fix BytePlus so that failed requests (like rate limits) are reported as real errors instead of looking like an empty successful response

Why

Three unrelated bugs that caused confusing, silent failures: shell commands breaking on quoted text, typed messages vanishing on tab switch, and BytePlus errors being swallowed so failures looked identical to empty responses.

Closes #384 , #382

How to test

• Run a run_shell action with shell: "cmd" and a command containing a quoted argument, e.g. claude -p "test prompt", in both foreground and background mode. Confirm it runs correctly instead of failing or mangling the argument.
• Type a draft message in the Chat tab, switch to another tab (Settings or Tasks & Actions), then switch back. Confirm the draft is still there.
• Trigger a BytePlus call that fails (e.g. hits a rate limit). Confirm the failure now shows up as a proper error instead of looking like an empty response.