MV1: move contracts and sdk under modules/, importers follow

The delivery repository's contracts and SDK live under modules/ as
mesh-delivery-contracts and mesh-delivery-sdk, their Go module paths
renamed to match the folders (the TypeScript names already did), and
every importer in mesh-delivery, mesh-catalog, mesh-host, mesh-tools
and mesh-sdk follows in the same group: a design as it should be, one
path per module, checked by the group's check building every importer.

Builds: design 47 G §427, §88

Claude-Session: https://claude.ai/code/session_01NcbgfGKaxw984XyAPfLm4h

modules/mesh-delivery-forge-bridge/internal/gitfixture/gitfixture.go

@@ -1,4 +1,4 @@
-// Package gitfixture reads the seat git's own fixtures (contracts/seats/git/fixtures/verbs.json), so the bridge's unit
+// Package gitfixture reads the seat git's own fixtures (modules/mesh-delivery-contracts/seats/git/fixtures/verbs.json), so the bridge's unit
 // fakes answer what the seat's holder answers and nothing the contract does not say (design 47 *The seat `git`*).
 package gitfixture
 
@@ -22,7 +22,7 @@ func All(t testing.TB, name, of string) []json.RawMessage {
 func Seat(t testing.TB, seat, file, name, of string) []json.RawMessage {
 	t.Helper()
 	_, here, _, _ := runtime.Caller(0)
-	raw, err := os.ReadFile(filepath.Join(filepath.Dir(here), "../../../../contracts/seats", seat, "fixtures", file+".json"))
+	raw, err := os.ReadFile(filepath.Join(filepath.Dir(here), "../../../mesh-delivery-contracts/seats", seat, "fixtures", file+".json"))
 	if err != nil {
 		t.Fatal(err)
 	}