v1.12.0 — Quality Scale conformance (Bronze + Silver/Gold picks)

Backend brought to Integration Quality Scale patterns (custom integrations are not
formally graded; progress is tracked in custom_components/houseplan/quality_scale.yaml):

• entry.runtime_data (typed HouseplanData: both stores + the write lock) replaces
  hass.data[DOMAIN] for entry data; WS handlers resolve it per call and answer
  not_ready while no entry is loaded. New store.py common module.
• test-before-setup: storage readability is verified in async_setup_entry
  (ConfigEntryNotReady on failure). Unloading is supported; WS commands and
  static paths are global by design (documented).
• single_config_entry: true in the manifest replaces the manual flow check.
• Store versioning: stores now carry minor_version and a migration hook
  (HouseplanStore._async_migrate_func) — schema changes get a single upgrade path.
• Diagnostics (diagnostics.py): redacted dump (options, rev, per-space stats,
  markers with personal fields redacted, layout size).
• Repairs: a missing plan file raises a repair issue (broken_plan) with
  en/ru translations; issues clear automatically when resolved.
• System health (system_health.py): rev, spaces/rooms/markers/layout counters.
• Uninstall cleanup: async_remove_entry deletes our Lovelace resource entry.
• Tests: config flow, WS API (layout ops, rev conflict, not_ready, plan upload
  validation), HTTP upload (ok/bad ext/traversal) on pytest-homeassistant-custom-component
  — run in CI on Python 3.13; pure validation tests still run anywhere.
• strings.json added; translations updated.