Import march-2020-03-10 from private repo (scrubbed 2026-05-27)

Targets Rec Room 2020.03.10 client (also serves 2020.03.06).

Re-import after adding:
- DorkNet.ClientMod/dorknet-clientmod.json.template — config schema
  the launcher's manifest-driven patcher renders into UserData/.
- tools/build-patcher-zip.ps1 — produces dorknet-clientpatch-{key}.zip
  for v1-march-* Release uploads.
- .github/workflows/release.yml — on tag push publishes both
  dorknet-server-march_2020_03_10-win-x64.zip and
  dorknet-clientpatch-march_2020_03_10.zip as Release assets.

Same scrub rules as december; tools/build-patcher-zip.ps1 added to
the maintainer-side allow-list so it survives.

DorkNet.Server/Migrations/20260516205306_MakeRoomDataBlobBytesNullable.cs

@@ -0,0 +1,50 @@
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace DorkNet.Server.Migrations
+{
+    /// <inheritdoc />
+    public partial class MakeRoomDataBlobBytesNullable : Migration
+    {
+        // CRITICAL: this migration must NOT drop or recreate the Bytes
+        // column. The column physically exists on every prod DB and
+        // holds the legacy bytes that haven't been backfilled to S3
+        // yet. A DropColumn here would obliterate every pre-cutover
+        // room save. We only flip NOT NULL -> NULL so new inserts
+        // (which leave the property null because writers go S3-only
+        // now) don't crash on the constraint. Run the
+        // /api/admin/v1/storage/backfill admin endpoint to copy the
+        // bytes from this column into S3 row-by-row; a follow-up
+        // migration drops the column once every row has been moved.
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.AlterColumn<byte[]>(
+                name: "Bytes",
+                table: "RoomDataBlobs",
+                type: "BLOB",
+                nullable: true,
+                oldClrType: typeof(byte[]),
+                oldType: "BLOB");
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            // Re-tighten to NOT NULL. Any rows that became NULL during
+            // the backfill won't pass this constraint — caller's
+            // responsibility to repopulate or delete those rows
+            // before rolling back. Defaulting to empty BLOB keeps
+            // the constraint satisfiable.
+            migrationBuilder.AlterColumn<byte[]>(
+                name: "Bytes",
+                table: "RoomDataBlobs",
+                type: "BLOB",
+                nullable: false,
+                defaultValue: new byte[0],
+                oldClrType: typeof(byte[]),
+                oldType: "BLOB",
+                oldNullable: true);
+        }
+    }
+}