Merge upstream/main: KartaView provider meets i18n

Upstream's KartaView PR (#1121) extracted the Mapillary coverage engine
into a shared lineCoverage.js and made the panel wording
provider-specific (coverage noun/action, SINCE upload-date note,
highlightsSequence legend gate), again in the regions this branch
localizes.

- mapillary/coverage.js: taken as upstream's thin re-export of the new
  lineCoverage.js; the generic too-high hint stays msg()-marked, now in
  lineCoverage.js where the default lives.
- kartaview/policy.js: coverage hints (tooHigh, noCoverage) marked as
  msg() data so they translate like every other coverage hint; thrown
  error messages stay English, matching the Mapillary precedent.
- presentMeta: KartaView counts streets, and Russian plurals need the
  noun inside the template, so the count line gets its own literal tn
  pair keyed off coverageLabel.noun, falling back to the sequences pair;
  upstream's noun/action data contract is untouched.
- uiState legend: upstream highlightsSequence gate with t('Selected');
  sinceNote localized with a {names} placeholder.
- layer-panels.html: sl-since-note wiring kept, data-i18n hooks kept.
- CHANGELOG: both sides kept. es/ru: 4 new keys each.

npm run i18n complete (953 messages each); npm test 6504/6506 (the one
failure is the pre-existing environmental OPENAI_API_KEY leak in
devFreshDotenv, unrelated); build passes.

src/layers/streetLevel/uiState.js

@@ -18,6 +18,9 @@ import { msg, t } from '../../i18n/index.js';
  * @property {string} color   The source's one colour.
  * @property {boolean} [groundClick]
  * @property {Array<'pano'|'since'>} [filters]
+ * @property {{noun: string, action: string}|null} [coverageLabel]
+ * @property {boolean} [highlightsSequence]   Its lines turn cyan when their sequence is selected.
+ * @property {'capture'|'upload'} [sinceBasis]   What its SINCE compares.
  */
 
 /**
@@ -35,6 +38,8 @@ export function summarizeCoverage(providers) {
         ? msg('No street-level imagery providers configured')
         : [...new Set(active.map((p) => p.hint).filter(Boolean))].join(' · '),
     error: active.find((p) => p.error)?.error || null,
+    // One source is lit at a time; its wording counts the lines.
+    label: active.find((p) => p.coverageLabel)?.coverageLabel || null,
     keyRequired:
       active.length > 0 && active.every((p) => p.keyRequired === true),
     keyRejected:
@@ -69,6 +74,20 @@ export function filterControls(providers) {
   return { pano: honoured('pano'), since: honoured('since') };
 }
 
+/**
+ * The note under SINCE when a lit provider dates its imagery by upload,
+ * e.g. "KartaView: by upload date", or null.
+ * @param {Array<ProviderSnapshot>} providers
+ */
+export function sinceNote(providers) {
+  const names = providers
+    .filter((p) => p.on && p.sinceBasis === 'upload')
+    .map((p) => p.name);
+  return names.length
+    ? t('{names}: by upload date', { names: names.join(', ') })
+    : null;
+}
+
 /**
  * The panel snapshot from core state and provider snapshots. The legend has
  * one swatch per active source that draws coverage lines, then Selected.
@@ -93,7 +112,13 @@ export function composeUIState({
       label: provider.name,
       color: provider.color,
     }));
-  if (legend.length)
+  // "Selected" only beside a source whose lines turn cyan when selected.
+  if (
+    active.some(
+      (provider) =>
+        provider.groundClick !== true && provider.highlightsSequence !== false,
+    )
+  )
     legend.push({ key: 'selected', label: t('Selected'), color: COLORS.selected });
   return {
     enabled,
@@ -103,6 +128,7 @@ export function composeUIState({
     keyRejected,
     filter: { ...filter },
     filterControls: filterControls(providers),
+    sinceNote: sinceNote(providers),
     providers: providers.map((p) => ({ ...p })),
     coverage,
     legend,