refactor(street-level): simpler panel — native fullscreen, no FOLLOW button, no provider chips

EXPAND now uses the browser's Fullscreen API on the viewer element, which
stays in the panel; the hand-built modal (re-parenting to <body>, inert
siblings, focus trap, document-level Esc/Tab, Clean View/recording/cockpit
hide rules) is gone. The button is hidden where the API is missing.

The FOLLOW button and the PROVIDERS chip row are removed. The header pill is
the only layer switch and re-enables a provider switched off elsewhere; under
KEY REQUIRED the error line says which key to add. Chip colour support in
chipGroup, dead CSS and tests pinning the removed behaviour go with them.

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

README.md

@@ -296,7 +296,7 @@ Twenty layers and map sources. **Seventeen have a keyless path.** Some offer add
 | 🚗 **Traffic**              | Simulated vehicles on OSM roads. With TomTom, live flow speeds drive the simulation and congestion colors below ~8 km; individual vehicle positions are not live observations                                                                                                                                                                                                       | TomTom + OSM                            | 🟢 simulation · 🟡 live flow speeds                                                                 |
 | 📹 **CCTV Mesh**            | ~3,900 public cameras projected _into_ the 3D space — Austin · Texas (TxDOT) · California (Caltrans) · London (TfL) · Ontario (511) · Finland (Fintraffic) · British Columbia (DriveBC) · Estonia (Tallinn, Tarktee) · Delaware (DelDOT live video) · New South Wales (Live Traffic NSW) · Calgary · Norway (Statens vegvesen). Positions are published; poses are estimated priors **you calibrate by dragging a gizmo on the camera itself** | City APIs                               | 🟢                                                                                                  |
 | 📷 **Mapped ALPR Cameras**  | License-plate-reader camera locations tagged by OpenStreetMap contributors, loaded one city-sized view at a time, with **SHOW NEAREST**. Locations and tags only: no plate data, no video                                                                                                                                                                                           | OpenStreetMap (incl. DeFlock mapping)   | 🟢                                                                                                  |
-| 📷 **Street Level**         | Street-level photos behind one panel, one chip per provider: coverage on the streets, image cones, an embedded viewer and **FOLLOW**. Mapillary first; Panoramax, KartaView and Google Street View planned                                                                                                                                                                          | Mapillary                               | 🟡 Mapillary client token                                                                           |
+| 📷 **Street Level**         | Street-level photos behind one panel: coverage on the streets, image cones and an embedded viewer with full-screen **EXPAND**. Mapillary first; Panoramax, KartaView and Google Street View planned                                                                                                                                                                          | Mapillary                               | 🟡 Mapillary client token                                                                           |
 | 📻 **Radio**                | Geolocated world radio with an **analog tuner** — drag the needle across up to 750 stations and the globe flies to each broadcaster                                                                                                                                                                                                                                                 | Radio Browser / broadcasters            | 🟢                                                                                                  |
 | 🚌 **Transit**              | Live buses, trams, metros, trains and ferries with delayed playback between reports, selected-vehicle trails, and mode-coloured DETECT labels — Boston, Austin, Minneapolis, Helsinki, the Netherlands, Norway, South East Queensland                                                                                                                                               | Operator GTFS-Realtime feeds            | 🟢                                                                                                  |
 | 🚲 **Bikeshare**            | Live station availability                                                                                                                                                                                                                                                                                                                                                           | GBFS                                    | 🟢                                                                                                  |
@@ -338,7 +338,7 @@ _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**.
 
-**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). The **IMAGERY** (ALL / 360° / FLAT) and **SINCE** filters apply to every provider. Click a coverage line for its image cones and a cone to open the photo. Above the photo: **EXPAND**, **FIT / FILL**, 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 "© Mapillary contributors, CC BY-SA 4.0" while Mapillary is on.
+**Use.** Turn on **Street Level** under DATA LAYERS → Cameras, or with the pill in the STREET LEVEL panel header. Each provider draws in its own colour (Mapillary green; see the legend). The **IMAGERY** (ALL / 360° / FLAT) and **SINCE** filters apply to every provider. Click a coverage line for its image cones and a cone to open the photo. Above the photo: **EXPAND** (full screen; Esc leaves) and **FIT / FILL**. The caption links to the image on the provider's site, and the globe credits "© Mapillary contributors, CC BY-SA 4.0" while Mapillary is on.
 
 Share links carry the provider switches and filters (`0.m.0` Mapillary off, `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`.