feat(street-level): movable, simplified panel with the photo first

- The viewer opens at the top of the panel, under the header, so the photo
  is on screen without scrolling; its tools (EXPAND, FIT/FILL, FOLLOW, close)
  sit in a bar above the image, clear of the provider's own overlays, and the
  caption wraps instead of truncating.
- No separate ON/OFF or OPEN NEAREST PHOTO buttons: the header pill is the
  layer switch, and a provider chip is lit only while the layer is on (the
  last lit chip switches the layer off).
- SINCE is a stepped slider (any date to the last month) whose readout names
  the cut-off date and is announced via aria-valuetext.
- The panel floats and resizes (portable spec); in a resized window the
  viewer takes the spare height and only the settings scroll. SHRINK after
  EXPAND, collapsing, or a header double-click docks it at its default size.
- FIT/FILL tooltips say what they do.

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

README.md

@@ -336,7 +336,9 @@ Setup for Mapillary:
 
 Without the token the STREET LEVEL panel reads **KEY REQUIRED**, the Mapillary chip turns amber and the controls stay greyed out.
 
-Turn on **Street Level** under DATA LAYERS → Cameras, or open the STREET LEVEL strip in the right rail. The **PROVIDERS** row has one chip per registered provider; switch a provider off and its coverage, its on-globe credit and its share-link bit go with it. The **IMAGERY** filter (ALL / 360° / FLAT) and the **SINCE** window apply to every provider at once. Mapillary's coverage draws as ground-hugging lines (recent captures bright green, older ones dim, 360° panoramas magenta); click a line for its image cones and a cone to open the photo in the embedded viewer, or press **OPEN NEAREST PHOTO** for the closest image to the view centre. **EXPAND** grows the viewer to most of the screen and **CAMERA FOLLOWS VIEW** drives the globe camera from the panorama; the caption links to the image on the provider's own site. Mapillary blurs faces and licence plates before publishing imagery, and the globe credits "© Mapillary contributors, CC BY-SA 4.0" while the provider is on.
+Turn on **Street Level** under DATA LAYERS → Cameras, or open the STREET LEVEL strip in the right rail and press the **ON/OFF** pill in its header. The **PROVIDERS** row has one chip per registered provider: lighting a chip turns its imagery on (and the layer with it), and darkening the last lit chip turns the layer off. The **IMAGERY** filter (ALL / 360° / FLAT) and the **SINCE** slider (any date on the left, the last month on the right, with the cut-off date spelled out) apply to every provider at once. Mapillary's coverage draws as ground-hugging lines (recent captures bright green, older ones dim, 360° panoramas magenta); click a line for its image cones and a cone to open the photo. The photo opens at the top of the panel, so it is on screen without scrolling. The bar above it has **EXPAND** (most of the screen), **FIT** (the whole photo, with dark bars where its shape differs from the frame) / **FILL** (edge to edge, cropped) and **FOLLOW** (the globe camera moves wherever the street-level view looks); the caption links to the image on the provider's own site. Mapillary blurs faces and licence plates before publishing imagery, and the globe credits "© Mapillary contributors, CC BY-SA 4.0" while the provider is on.
+
+The panel is also a window: drag its header to lift it out of the rail, and resize it from any edge or corner. A larger window gives the photo the room; only the settings below it scroll. Double-clicking the header, collapsing the window, or pressing SHRINK after EXPAND puts it back in the rail at its default size, so it never stays parked over the globe.
 
 Share links carry the layer's provider switches and filter (`3.m.0` turns Mapillary off, `3.p.p` keeps only panoramas, `3.s.365` shows the last year). Adding a provider means implementing the contract in `src/layers/streetLevel/registry.js` and registering it in `src/app/layers/streetLevel.js`; the chip, credit and share bit follow.