[EPIC] Contain CAMS coupling & dependency drift

29 of ~80 files touch CAMS types; `AppTaskController()` is called raw from 8+ places including the router and view-model getters, the UI hardcodes `UserTaskState` mappings, and the `Sensing` facade leaks executor internals. Each CAMS major bump (the 2.x migration in #601/#571) currently fans out across the whole app.

Goal: CAMS churn is absorbed in `Sensing`/`CarpBackend`/one task facade, and dependency constraints are deliberate.

**Definition of done:** no `AppTaskController()`/executor access outside the facades; pubspec has no `any` constraints.

Line references are against branch `chore/cams-2.x-upgrade` @ 560a181.