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]>

README.md

@@ -344,7 +344,7 @@ _The Space Missions layer replaying a Falcon 9 ascent — labeled `RECONSTRUCTED
 
 **Setup.** At [mapillary.com/dashboard/developers](https://www.mapillary.com/dashboard/developers), register an application with **Read** access and copy its **Client Token** (`MLY|…`). Paste it into **POWER UP → Mapillary**, or set `MAPILLARY_CLIENT_TOKEN` in `.env` and restart. Without it the panel reads **KEY REQUIRED**. **Google Street View** uses `GOOGLE_MAPS_API_KEY` with the **Maps JavaScript API** enabled for it in Google Cloud; its chip starts off, since every panorama is billed to the key. **KartaView** and **Panoramax** need nothing: their public APIs are keyless.
 
-**Use.** Turn on **Street Level** under DATA LAYERS → Cameras, or with the pill in the STREET LEVEL panel header. Each provider has a chip in its own colour (Mapillary green), and one is lit at a time: lighting one switches the others off. Mapillary, which is free, is lit by default. The **IMAGERY** (ALL / 360° / FLAT) and **SINCE** filters apply to Mapillary; Street View panoramas are all 360°, so with Street View lit the filters and legend are hidden. Click a coverage line for its image cones and a cone to open the photo. Light **KARTAVIEW** (purple) and zoom in below about 6 km: its lines are the streets KartaView has photos of, and a click on one opens the photo nearest the click, flat or 360° (drag to look around), with cones along its drive; **‹ ›** or ← → step through the drive (Shift+← →, ↑ ↓ and + − look around a 360° photo; pinch zooms on a phone). Photos KartaView has archived are skipped, and where all are archived the panel says so. KartaView photos are undated on its map, so the filters do not apply to it. Light **PANORAMAX** (orange) for the open, federated commons (strongest in France and Belgium): from orbit its dots show where it has pictures, and below about 30 km its lines are sequences. A click on a line opens that sequence's picture nearest the click without moving the camera, flat or 360°, with cones along the sequence around it; **‹ ›** or ← → step through it, and both filters apply. Its caption names the picture's author and licence (mostly CC BY-SA 4.0; IGN's are Licence Ouverte 2.0). On the **Google 3D** map (Google's terms keep Street View off other maps, where it does not appear), light **GOOGLE STREET VIEW** and click a street from below 3 km, or press **OPEN STREET VIEW** for the view centre, to open Google's panorama there; step along its arrows. Above the photo: **EXPAND**, **FIT / FILL** (Mapillary, and flat KartaView and Panoramax photos), and **FOLLOW** (the globe camera follows the photo's view; Google 3D map only). The caption links to the image on the provider's site, and the globe credits each provider that is on ("© Mapillary contributors, CC BY-SA 4.0", "Street View imagery © Google", "© KartaView contributors, CC BY-SA 4.0", "© Panoramax contributors, licence per picture"). KartaView's own photo pages fail for signed-out visitors, so its link opens the full-size photo.
+**Use.** Turn on **Street Level** under DATA LAYERS → Cameras, or with the pill in the STREET LEVEL panel header. Each provider has a chip in its own colour (Mapillary green), and one is lit at a time: lighting one switches the others off. Mapillary, which is free, is lit by default. The **IMAGERY** (ALL / 360° / FLAT) and **SINCE** filters apply to Mapillary; Street View panoramas are all 360°, so with Street View lit the filters and legend are hidden. Click a coverage line for its image cones and a cone to open the photo. Light **KARTAVIEW** (purple) and zoom in below about 6 km: its lines are the streets KartaView has photos of, and a click on one opens the photo nearest the click, flat or 360° (drag to look around), with cones along its drive; **‹ ›** or ← → step through the drive (Shift+← →, ↑ ↓ and + − look around a 360° photo; pinch zooms on a phone). Photos KartaView has archived are skipped, and where all are archived the panel says so. KartaView photos are undated on its map, so the filters do not apply to it. Light **PANORAMAX** (orange) for the open, federated commons (strongest in France and Belgium): from orbit its dots show where it has pictures, and below about 60 km its lines are sequences. A click on a line opens that sequence's picture nearest the click without moving the camera, flat or 360°, with cones along the sequence around it; **‹ ›** or ← → step through it, and both filters apply. Its caption names the picture's author and licence (mostly CC BY-SA 4.0; IGN's are Licence Ouverte 2.0). On the **Google 3D** map (Google's terms keep Street View off other maps, where it does not appear), light **GOOGLE STREET VIEW** and click a street from below 3 km, or press **OPEN STREET VIEW** for the view centre, to open Google's panorama there; step along its arrows. Above the photo: **EXPAND**, **FIT / FILL** (Mapillary, and flat KartaView and Panoramax photos), and **FOLLOW** (the globe camera follows the photo's view; Google 3D map only). The caption links to the image on the provider's site, and the globe credits each provider that is on ("© Mapillary contributors, CC BY-SA 4.0", "Street View imagery © Google", "© KartaView contributors, CC BY-SA 4.0", "© Panoramax contributors, licence per picture"). KartaView's own photo pages fail for signed-out visitors, so its link opens the full-size photo.
 
 Drag the panel header to float the panel, and resize it from any edge. Double-click the header or collapse it to put it back in the rail. Share links carry the provider switches and filters (`0.m.0` Mapillary off, `0.m.0_0.r.google-1` Street View on, `0.m.0_0.r.kartaview-1` KartaView on, `0.m.0_0.r.panoramax-1` Panoramax on (a link that leaves out `m` keeps Mapillary, the default, lit), `0.p.p` panoramas only, `0.s.365` the last year). To add a provider, implement the contract in `src/layers/streetLevel/registry.js` and register it in `src/app/layers/streetLevel.js`.