chore: scaffold progression domain + test projects (slice 0)

net8.0 classlib, no engine ref, EnableDynamicLoading; xunit test project
referencing domain only; excluded from Godot's **/*.cs glob; .gdignore both

docs/plans/phase-a-progression-domain.md

@@ -37,8 +37,14 @@ No tests. Pure setup.
 
 **Done when:** `dotnet test` runs and reports zero tests; Godot still builds; the game still launches and plays.
 
-**Guard rail for the whole phase:** `grep -r "using Godot" progression/` must stay empty. That single check is
-what ADR-0004 buys you.
+**Guard rail for the whole phase:**
+
+```sh
+grep -rn "using Godot" progression progression.tests --include=*.cs   # must print nothing
+```
+
+That single check is what ADR-0004 buys you. Scope it to `--include=*.cs` — an unscoped `grep -r` also matches
+prose in the `.csproj` comments and reports a false violation.
 
 ---