Puffer Card v1.2.2

Fixed

• Blank chart area and page reload required to recover. Three root causes:
  1. The refresh logic ran inside updated(), which Lit calls after every
     reactive property change. Setting _histLoading = true triggered a
     re-render, which triggered updated() again while hass kept updating
     in the background, causing cascading fetch calls.
  2. There was no concurrency guard: two _fetchHistory() calls running in
     parallel would write to _history and _histLoading out of order,
     producing inconsistent state visible as repeated flickering followed by
     a blank chart.
  3. Any network/API error inside _fetchHistory() left _histLoading
     permanently set to true, showing only the loading placeholder.
     The fetch cycle is now driven by setInterval started in
     connectedCallback and cleared in disconnectedCallback. A _fetching
     flag prevents concurrent calls, and a try/finally block ensures
     _histLoading is always reset even on error.