Merge origin/i18n-spanish: whole-interface translation meets KartaView

This branch moved twice at once: upstream merged KartaView (#1121, a
third keyless street-level provider sharing a new lineCoverage.js), and
the remote i18n-spanish gained the whole-interface translation work
(1993 catalog entries, translateKnown, data-i18n-runtime, the unmarked-
string detector in npm run i18n) built on the Street View merge.

Integration keeps the remote's mechanisms and re-adds KartaView on top:

- presentMeta: remote's translateHint for coverage hints, plus the
  KartaView count line as its own literal tn pair (Russian plurals need
  the noun inside the template; keyed off coverageLabel.noun with the
  sequences pair as the default).
- uiState: upstream's highlightsSequence legend gate (KartaView's lines
  do not highlight) with t('Selected').
- layer-panels.html: remote's data-i18n/data-i18n-runtime hooks plus the
  sl-since-note wiring KartaView's upload-date SINCE note needs.
- kartaview viewer: the photo-navigation aria-label and img alt go
  through t(), as the remote's unmarked-string detector requires.
- catalogs: remote's 1987-entry base (its refined keys supersede this
  branch's earlier Street View wording) plus the KartaView entries:
  coverage hints, the upload-date note, the streets count line (with
  Russian one/few/many/other forms) and the viewer strings.

npm run i18n: complete, no unmarked strings. npm test: 6520/6522 (the
one failure is the pre-existing environmental OPENAI_API_KEY leak in
devFreshDotenv). Build passes.

docs/CURRENT-STATE.md

@@ -3065,8 +3065,11 @@ Shipped locales: **en** (source and fallback), **es** and **ru**. The code lives
 - **Not translated by design:** layer ids, share-link and hash parameters, API
   fields, voice tool schemas, provider names, feed data (callsigns, vessel and
   station names) and attribution.
-- **Gaps.** Strings added after #601's extraction (for example the Street Level
-  panel) are still raw English; there is no lint for unmarked UI text yet.
+- **Unmarked text.** The same check lists UI text that is not marked at all
+  (markup without `data-i18n*`, literals reaching the page without `t`/`tn`/`msg`)
+  and fails on it. Text kept on purpose says why: `translate="no"`,
+  `data-i18n-runtime`, or `// i18n-ignore: <reason>`. `src/tools/` is skipped:
+  it writes for AI clients, not the page.
 
 ## Canonical Docs Order