Merge upstream/main: Street View rework meets i18n

Upstream's Street View rework (second imagery provider, one source at a
time, OPEN STREET VIEW button, key-alternative guidance) rewrote exactly
the street-level regions this branch localizes.

Resolved as upstream logic + re-applied localization:

- keySetupCore: new unlock copy kept as msg() data; added
  keySetupAlternativeKeyNames() returning machine values (registry key
  names) so key-setup core stays English while presentation localizes.
- New src/ui/keyGuidance.js: localized key-guidance composer shared by
  layerPanel and streetLevelPresentation (requirement sentence plus the
  "or light X to use your Y key" alternatives tail, placeholders only).
- streetLevelPresentation: keyGuidance()/presentNearest()/presentMeta
  relocalized (t/tn + formatNumber instead of toLocaleString);
  renderModes and month-precision dates kept from upstream.
- layer-panels.html: upstream row ids, sl-meta-row and the new button
  kept, data-i18n hooks re-applied (incl. OPEN STREET VIEW fallback).
- es/ru catalogs: 13 new keys, stale unlock key replaced in place.

npm run i18n: complete for es and ru. npm test: 6345/6347; the one
failure (devFreshDotenv provenance) also fails on plain upstream/main
and on the pre-merge tip here - this machine leaks OPENAI_API_KEY into
spawned children with a replaced env, so it is environmental.

src/ui/keyGuidance.js

@@ -0,0 +1,45 @@
+import {
+  keySetupAlternativeKeyNames,
+  keySetupRequirementEnvVars,
+} from '../keySetupCore.mjs';
+import { t } from '../i18n/index.js';
+
+// Localized key-guidance sentences. keySetupCore owns the machine values
+// (env-var names, registry titles) because it also runs in node-side
+// key-setup builds that stay English; this presentation boundary owns the
+// sentences, composed with placeholders so word order can differ per language.
+
+/** The Provider Settings hint for a missing key, or '' for a hidden key. */
+export function keyRequirementText(requiresKeyId) {
+  const envVars = keySetupRequirementEnvVars(requiresKeyId);
+  return envVars
+    ? t('Needs {envVars} — add it in Provider Settings', { envVars })
+    : '';
+}
+
+/**
+ * A requirement sentence, plus the switched-off sources that would draw with
+ * a key already set.
+ * @param {string} requirement What `keyRequirementText` said ('' allowed).
+ * @param {Array<{label: string, requiresKeyId?: string|null}>} [alternatives]
+ */
+export function withKeyAlternatives(requirement, alternatives = []) {
+  if (!alternatives.length) return requirement;
+  const named = keySetupAlternativeKeyNames(alternatives);
+  const option = ({ label, name }) =>
+    name
+      ? t('light {label} to use your {name} key', { label, name })
+      : t('light {label}', { label });
+  if (requirement)
+    return t('{requirement}, or {offer}', {
+      requirement,
+      offer: named.map(option).join(t(', or ')),
+    });
+  // No requirement: the offer stands alone, so it opens with a capital.
+  const { label, name } = named[0];
+  const lead = name
+    ? t('Light {label} to use your {name} key', { label, name })
+    : t('Light {label}', { label });
+  const tail = named.slice(1).map(option).join(t(', or '));
+  return tail ? t('{lead}, or {tail}', { lead, tail }) : lead;
+}