Add NYC subway Transit view

[kyleve]

Summary

• enable Transit as Throw’s second projection experience, starting with NYC Subway data from the official MTA supplemented GTFS schedule and all eight GTFS-Realtime partitions
• estimate assigned trains along scheduled shapes, preserve per-partition last-good data during retries, and render route-colored network lines, train marks, destinations, and contextual stops
• add Transit setup and settings, independent map radius/center/appearance preferences, version-three preference migration, and activation/rotation integration
• keep the transit contracts agency-neutral so another city, such as San Francisco, can supply its own schedule and realtime adapters without changing projection semantics
• add protobuf generation provenance, SwiftProtobuf and ZIPFoundation attribution, focused unit coverage, and projector/settings snapshots

Correctness and architecture

• ThrowSession owns one injected TransitRuntime; only active or prewarming experiences may poll
• static schedule work and realtime decoding run off the main actor, with generation checks preventing late frames from becoming visible
• valid empty feeds satisfy activation readiness, while partial partition failures retain only bounded last-good data
• typed TransitMapViewport enforces the 5–50 NM product invariant before values reach persistence or projection
• configuration and removal update preferences and playlists transactionally

Verification

• ./ide --no-open
• ./test ThrowCoreTests ThrowUITests — 369 tests passed
• selected Throw snapshot suites — passed
• ./swiftformat --lint
• ./sf-symbols --lint
• ./xcstrings --lint
• ./attribution --check
• architecture validation — no violations
• visually reviewed Transit projector snapshots at 16:9, 16:10, and 4:3, plus setup/configured settings snapshots

Stacked on #293.