feat(strommix): hero variant, 24h sparkline, trend, polishing

- New "hero" variant between compact and full: pct + status +
  sparkline + trend, no sub-cards or accordion
- 24h Wind+Solar sparkline below hero pct, accent-colored
- Trend arrow vs previous hour with delta percentage points
- Polling pauses on tab hidden, refetches on visibility return
  if last fetch >5min old
- Skeleton loader replaces "Lade…" text (matches final layout)
- Retry button on error state (silent vs explicit fetch)
- Stale-flag now prominent red badge in header bar
- Stand-time wrapped in <time datetime title> for full-date hover
- loadMw=0 falls back to last hourly slot instead of red error
- Negative-price banner replaces standalone price card (dedup)
- Production breakdown grid: clean auto/1fr label-value alignment
- Print CSS: details auto-open, chevrons hidden
- All German strings moved to translation keys
- STROMMIX_DEFAULT_THRESHOLDS const as single source for buckets

Includes data-block="LiveStrommix" attribute for the new
identifier scheme + new RenewableSparkline.svelte component.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/lib/translations.ts

@@ -114,6 +114,28 @@ const TRANSLATION_KEYS = [
   "calendar_time_suffix",
   "calendar_select_day",
   "calendar_next_events",
+  "calendar_all_upcoming",
+  "calendar_today",
+  "calendar_tomorrow",
+  "calendar_in_days",                // {{n}}
+  "calendar_no_future_events",
+  "calendar_clear_filter",
+  "calendar_event_count",            // {{n}}
+  "calendar_add_to_google",
+  "calendar_download_ics",
+  "calendar_open_maps",
+  "calendar_show_past",
+  "calendar_hide_past",
+  "calendar_past_events",
+  "calendar_filter_by_tag",
+  "calendar_all_tags",
+  "calendar_multi_day_range",        // {{from}}, {{to}}
+  "calendar_starts_in",               // {{n}}
+  "calendar_starts_in_minutes",       // {{n}}
+  "calendar_running_now",
+  "calendar_jump_to_month",
+  "calendar_today_marker",
+  "calendar_untitled",
   "calendar_show_more",
   "calendar_show_less",
   "post_overview_all",
@@ -207,6 +229,17 @@ const TRANSLATION_KEYS = [
   // Compact variant for homepage / sidebar.
   "strommix_compact_label",         // {{pct}}, {{status}}
   "strommix_compact_more",
+  // Akkordeon + history-panel headings.
+  "strommix_history_summary",
+  "strommix_residual_today_title",
+  "strommix_residual_today_desc",
+  // Loading / error UX.
+  "strommix_retry",
+  "strommix_trend_up",               // {{delta}}
+  "strommix_trend_down",             // {{delta}}
+  "strommix_trend_flat",
+  "strommix_sparkline_aria",         // {{from}}, {{to}}
+  "strommix_stale_badge",
 ] as const;
 
 export type TranslationKey = (typeof TRANSLATION_KEYS)[number];