API v2 add-on: studio sets, 360° spins and lifestyle scenes

Added

• API v2 add-on for keys with v2 access (access in /api/me: v2 or all). Cars with add-on images list groups on the trim endpoint next to views.
• Studio groups hero, steered, extra and drone: …/{trim}/{group} lists the images, …/{trim}/{group}/{image} resolves one.
• 360° spins in three rings (eye_level, low, high): …/{trim}/360 lists them, …/{trim}/360/{ring} returns every frame with its own signed image_url.
• Lifestyle scenes: …/{trim}/lifestyle, …/lifestyle/{scene} and …/lifestyle/{scene}/{image}.
• Add-on image options: lights=on, background (white, transparent or hex), paint color as hex (e.g. c8102e), windows=dark, plate=blank|logo, fit=contain|cover, size (2k … thumb) and hotspots=true (points of interest for interactive viewers).
• New errornotes for the add-on: G23, M24, L26, W28, N29, N30, O31, B32 — all listed in /api/errornotes.
• /api/me now shows access (v1, v2, all) and queue_priority; with the add-on also an addon section (formats, groups, options, brands, plate logo).
• With the add-on, /api/search finds add-on cars, /api/getall lists them with their groups, and a car's /colors, /features and /all describe its add-on options (any_hex_color, features.addon).
• /api/options, /api/sizes and /api/views add an addon section: the add-on options with their values, the size presets and the groups.
• Everything also works by stable id: /api/id/{id}/{group}/{image}, /api/id/{id}/360/{ring}, /api/id/{id}/lifestyle/{scene}/{image}.

Improved

• New images are produced in a fair queue: plans with higher priority go first, and identical requests arriving at the same time are produced only once.
• Recolouring many paints of the same view at once builds its paint mask once instead of for every colour — first loads under load are much faster and more reliable.
• Under very heavy load an image URL now answers 503 busy with Retry-After instead of timing out. Responses carry X-Cache and X-Queue-Wait-Ms.