test: guard both schema-delivery paths; fix playlist backfill defaults

Adds SchemaBootstrapParityTests, which closes the hole that let the
missing-column outage ship green. Every other test runs against a FRESH
database where EnsureCreated builds the whole model from the entities, so a
column that only exists in the model always appears — the failure mode is
invisible by construction. These two tests model an EXISTING database instead:

- Every model table/column must be reachable via a committed migration OR an
  idempotent Ensure* patch. Something covered by neither reaches only brand-new
  databases, and every query touching it throws on a deployed server.
- Anything added after the Initial migration must additionally appear as a
  Postgres ALTER/CREATE in DatabaseBootstrap, because that path is
  EnsureCreated-only and never replays migrations. This is precisely the rule
  PrivateInstances.RoomCode, Clubs.ClubChatEnabled and
  ChatMessages.ModerationState broke.

The first test asserts the union rather than migrations alone: a large amount of
schema legitimately predates the rule and lives only in the helpers. Tightening
that is separate cleanup; what must never happen is a column covered by nothing.

The helper-coverage parser reads the Ensure* SQL out of the source rather than
executing the private methods, and handles both C# string styles the file mixes
plus the loops that interpolate a column name (EnsureGameRewardColumnsAsync).

Also fixes a real data bug found in review: the Client2023WireFixes migration
backfilled SupportsJuniors/SupportsScreens/SupportsTeleportVR/SupportsWalkVR to
false for existing rows, while the entity default is true. A C# property
initializer is not a database default, so EF emitted false and every playlist
predating the migration would have been silently marked as not supporting
juniors, screens or either VR movement mode — the opposite of intent, and
inconsistent with the bootstrap helper, which already used true.

DorkNet.Server/Migrations/20260727200252_Client2023WireFixes.cs

@@ -51,7 +51,7 @@ namespace DorkNet.Server.Migrations
                 table: "Playlists",
                 type: "INTEGER",
                 nullable: false,
-                defaultValue: false);
+                defaultValue: true);
 
             migrationBuilder.AddColumn<bool>(
                 name: "SupportsLevelVoting",
@@ -65,21 +65,21 @@ namespace DorkNet.Server.Migrations
                 table: "Playlists",
                 type: "INTEGER",
                 nullable: false,
-                defaultValue: false);
+                defaultValue: true);
 
             migrationBuilder.AddColumn<bool>(
                 name: "SupportsTeleportVR",
                 table: "Playlists",
                 type: "INTEGER",
                 nullable: false,
-                defaultValue: false);
+                defaultValue: true);
 
             migrationBuilder.AddColumn<bool>(
                 name: "SupportsWalkVR",
                 table: "Playlists",
                 type: "INTEGER",
                 nullable: false,
-                defaultValue: false);
+                defaultValue: true);
 
             migrationBuilder.AddColumn<int>(
                 name: "WarningMask",