SchemaKit: snapshot format v2 and CodoMetis: annotation keys ship in 11.0.0; the 5.x format is read forever (D11) #58

Problem

Annotation keys and the snapshot format end up permanently in consumers' model snapshots and migrations. ROADMAP.md 5.5 (D11) plans one annotation per declaration, under the CodoMetis: prefix (owner-branded, so it survives any product name).

Changing the format in an 11.x minor would give every consumer an empty migration on a minor upgrade, which a CI gate on has-pending-model-changes reports as a failure. So the change belongs in 11.0.0.

Change

• SchemaKit writes v2 from 11.0.0 on. Previews may still change it.
• It reads the EFCore.ComplexIndexes 5.x blob forever, so a 5.x snapshot keeps diffing correctly after the package swap (SchemaKit: moving from EFCore.ComplexIndexes 5.x adds no migration, or exactly the one the guide documents #59).

Done when

• Round-trip tests pass for v2 and for a real 5.x snapshot (compiled with Roslyn, as SnapshotRoundTripTests does).
• The migration guide states up front the one empty migration the format change produces, if it produces one.
• It ships in 11.0.0.