WIP: feat(webui): expose Dream runs as read-only sessions

Summary

• expose Dream runs in the WebUI as a separate, localized, read-only, collapsible session group with date/time labels
• record and replay Dream reasoning, tool calls, file edits, streaming output, and file previews through the same thread UI as regular sessions
• render user messages as Markdown and preserve complete Dream history prompts without per-entry truncation
• allow Dream's restricted write_file tool to update only the canonical memory files when patch-based edits cannot apply

Testing

• python -m pytest tests/agent/test_dream.py tests/agent/test_turn_hooks.py tests/utils/test_webui_transcript.py -q
• python -m pytest tests/command/test_builtin_dream.py -q
• python -m pytest nanobot/channels/websocket/tests/test_websocket_channel.py::test_handle_file_preview_returns_workspace_file nanobot/channels/websocket/tests/test_websocket_channel.py::test_handle_file_preview_returns_workspace_file_for_dream_session -q
• npm run test -- --run src/tests/i18n.test.tsx src/tests/chat-list.test.tsx
• focused Ruff checks on the changed Python surfaces

Notes

• Browser verification is intentionally left for manual validation while this PR is in draft.