feat(street-level): camera follow only on the Google 3D map

FOLLOW puts the globe camera at eye height inside the street-level view; on
flat imagery or terrain there is nothing to stand among. The layer now takes
the application map stack controller (attachMapStackController), subscribes
to stack switches, offers FOLLOW only while the stack is 'photoreal', disables
the button with a MAP SOURCE hint elsewhere, and stops following when the
stack leaves Google 3D. Selection uninstall is a no-op when never installed.

The QA gate checks the disabled path and, when Google 3D is available, that
leaving it stops following; its caption-timeout dump now forces one render to
tell a missed update from a render fault.

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

README.md

@@ -336,7 +336,7 @@ 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 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.
+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; available on the Google 3D map only, since flat imagery has nothing to stand among); 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.