fix(street-level): Panoramax UX QA — connection budget, coverage to 60 km, Esc, attribution

From a UX QA round in the browser against the live API:
- A line click could time out while coverage loaded: the meta-catalogue
  speaks HTTP/1.1 only (six connections), and six tiles plus four
  searches queued the lookup behind megabyte tiles. Tiles now take
  three connections and searches two; a search that timed out is asked
  once more.
- Between 30 and ~100 km Paris read as empty: the density grid is ~10 km
  a cell. Lines now draw to 60 km (z10), as Mapillary's do; above, dots
  grow with the pictures they stand for.
- Esc in the docked viewer collapsed the whole panel instead of clearing
  the sequence the panel says it clears (shared photo viewer: KartaView
  too). The viewer now offers Esc to the provider first; expanded, the
  dialog keeps it.
- A picture whose producer is an email address is credited to the
  instance holding it (its `via` host), so Licence Ouverte pictures name
  their source.
- Empty states say why: "no Panoramax photos here match the filters"
  when the filter hid every line, and nothing to zoom into over empty
  sea. Wording follows KartaView's ("photos", "click a line for its
  nearest photo").

Co-Authored-By: Claude Opus 5.5 <[email protected]>

scripts/qa-street-level.mjs

@@ -1200,7 +1200,7 @@ async function main() {
             );
             assert.match(
               await page.$eval('#sl-coverage-meta', (node) => node.textContent),
-              /sequences in view · click a line for the photo there/,
+              /sequences in view · click a line for its nearest photo/,
             );
             await page.waitForFunction(
               () =>