Replay: deterministic record & playback (#4)

Add deterministic record/playback for a run.

Recording captures `(seed, config hash, ordered tick-tagged commands)` and re-simulates on playback — no state snapshots. `DotaFactory.exe --replay <file>` re-plays a recorded run view-only with manual speed/pause.

Reviewed-on: #4
Co-authored-by: Malte Langkabel <malte.langkabel@gmail.com>
Co-committed-by: Malte Langkabel <malte.langkabel@gmail.com>

src/lib/sim/BuildingSystem.h

@@ -23,6 +23,8 @@
 #include "ShipsConfig.h"
 #include "Tick.h"
 
+class Hasher;
+
 // Manages building placement, construction queuing, and the per-tick
 // production loop (belt→building pull, production, building→belt push).
 // All types including Belt and Splitter are stored as Building instances;
@@ -151,6 +153,11 @@ public:
     // Mutable iteration over all operational buildings.
     void forEachBuilding(std::function<void(Building&)> fn);
 
+    // -- Determinism ---------------------------------------------------------
+    // Folds all building, construction-site, and tile-occupancy state into the
+    // hasher in deterministic order (see docs/replay_design.md).
+    void appendChecksum(Hasher& hasher) const;
+
 private:
     const BuildingDef*  findBuildingDef(BuildingType type) const;
     const RecipeDef*    findRecipe(const std::string& id, BuildingType type) const;