Add desktop chat over WebSocket mirror

[pmbstyle]

Summary

Adds the Desktop chat client backed by the existing gateway WebSocket, and changes the WebSocket path into a mirror of the shared conversation history instead of a separate output channel.

What changed

• Mirrors inbound/outbound chat, worker events, progress, files, and typing state into the WebSocket session.
• Removes the old WebSocket-only response style/prompt behavior so other configured channels keep working while Desktop observes the same conversation.
• Adds the Desktop chat tab with message send, markdown rendering, image previews, paste/upload attachments, approvals, and thinking indicator.
• Stages Desktop chat attachments under workspace/tmp/desktop_chat and rejects WebSocket attachment paths outside that directory.
• Caps image preview generation at 25 MB so large selected files can be attached without reading the whole file into IPC state.
• Keeps WebSocket partial streaming compatible with existing internal_progress_send implementations while preferring emit_ws_progress when available.

Validation

• uv run pytest (910 passed, 1 skipped locally)
• uv run pytest tests/test_gateway_ws_resolution.py
• uv run pytest tests/test_router_tool_budget.py::test_plain_completion_can_stream_for_websocket tests/test_telegram_react_tag_sanitization.py::test_telegram_uses_reply_reaction_fallback_when_immediate_loses_tag tests/test_telegram_react_tag_sanitization.py::test_telegram_infers_reaction_from_short_text_edge_emoji -q
• uv run ruff check src/octopal/gateway/ws.py tests/test_gateway_ws_resolution.py
• uv run ruff check src/octopal/runtime/octo/router.py tests/test_telegram_react_tag_sanitization.py
• uv run black --check src/octopal/gateway/ws.py tests/test_gateway_ws_resolution.py
• uv run black --check src/octopal/runtime/octo/router.py tests/test_telegram_react_tag_sanitization.py
• npm run build from desktop/
• GitHub Actions PR Tests #269: success

[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	remark-gfm@​4.0.1
	react-markdown@​10.1.0

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