Initial commit: Theriapolis baseline at port/godot branch point

Captures the pre-Godot-port state of the codebase. This is the rollback
anchor for the Godot port (M0 of theriapolis-rpg-implementation-plan-godot-port.md).
All Phase 0 through Phase 6.5 work is included; Phase 7 is in flight.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Theriapolis.Core/Persistence/SaveMigrations/V7ToV8Migration.cs

@@ -0,0 +1,27 @@
+namespace Theriapolis.Core.Persistence.SaveMigrations;
+
+/// <summary>
+/// Phase 7 M0 — additive migration from save schema v7 (Phase 6.5 ship) to
+/// v8 (Phase 7 dungeons). Non-destructive: every v7 field carries over
+/// unchanged. Phase 7 reserves three new save sections — anchors, building
+/// deltas, and per-PoI dungeon state — but ships M0 with the version bump
+/// only; the fields default-initialise to empty and a v7 save loads as
+/// "no anchors persisted, no buildings modified, no dungeons visited"
+/// which is the truth for any pre-Phase-7 save.
+///
+/// Subsequent Phase 7 milestones (M1+) will populate these sections;
+/// the migration stays additive throughout.
+/// </summary>
+public sealed class V7ToV8Migration : ISaveMigration
+{
+    public int FromVersion => 7;
+    public int ToVersion   => 8;
+
+    public void Apply(SaveHeader header, SaveBody body)
+    {
+        // No data translation needed. Phase 7's new save sections
+        // (TAG_ANCHORS / TAG_BUILDINGS / TAG_DUNGEONS) default to empty in
+        // SaveBody and SaveCodec uses the established EOS-check pattern
+        // for additive sections. Pure version bump.
+    }
+}