Every event-derived ServerMessage gains sequence (global) and sessionSequence
(per-session) cursor fields. SessionSnapshot adds lastSequence and
lastSessionSequence at projection-read time. SnapshotComplete data object
terminates the snapshot phase and is registered in the polymorphic module.
replaySnapshot() now emits SnapshotComplete after all SessionSnapshot messages.
SessionStarted audit deferred with TODO comment. DomainEventMapper propagates
both cursors to all mapped messages including InferenceCompleted.
Deletes 21 Module.kt scaffolding objects that were never wired into any DI
registry. Removes unused imports across 8 production and 3 test files.
Restores StageExecutor, CyclePolicyResolver, PolicyValidation, and
ReplayContractTest — these are deferred features, not dead code.