fix(dashboard): relabel vacuum-extend diagnostics

[dacrypt]

Summary

• relabel the known siid 4 Mission Control diagnostics tiles so they show Cleaning Mode, Mop Mode, Waterbox Status, Task Status, Resume After Charge, and Carpet Boost instead of generic Unknown copy
• keep the raw values unchanged so the panel still works as a low-level debugging surface
• update BACKLOG.md with the shipped item, research notes, and the next planned follow-up

Why this is worth shipping

Users already have these vacuum-extend values in the dashboard, but the old labels hid useful meaning behind placeholder text. This is a small, safe UX win that makes diagnostics faster without changing any device behavior.

Research basis

• the official xiaomi.vacuum.c102gl MIoT spec still names these siid 4 properties as mop-mode, waterbox-status, task-status, break-point-restart, and carpet-press
• openhab/openhab-addons mirrors the same X20+ channel names, which reinforces the label mapping
• hass-xiaomi-miot issue #2767 still shows room-cleaning remains the riskier area, so this run stayed on a low-risk diagnostics improvement instead of action semantics

Tests

• added a dashboard regression test that fails on the old Unknown labels and passes with the new copy
• locally ran:
  • .venv/bin/python -m pytest tests/ -v
  • .venv/bin/ruff check src/ tests/
  • .venv/bin/ruff format --check src/ tests/
  • .venv/bin/mypy src/xiao/

Risk

Very low. Frontend copy only; no API, parsing, or device-control behavior changed.