replay: play back recorded runs via --replay (Phase 3)

Adds view-only playback: re-simulate from the recorded seed + commands and
verify the RNG checksums.

- ReplayReader (lib): parses a replay file into header + an ordered stream of
  command/checksum entries. CommandSerializer gains the inverse parseCommand
  (round-trips every verb; rejects malformed input).
- ReplayPlayer (lib): the playback driver. Applies each command at its exact
  recorded tick and verifies checksums in file order (start() handles tick 0;
  advanceTo(tick) handles each tick after sim.tick()). Independent of
  replay-time speed/pause; reports the first desync tick.
- CommandManager replay mode: enqueue() becomes a no-op so live input is
  ignored while the recorded stream drives application.
- main.cpp: --replay <file> reads + validates (warns on version/config-hash
  mismatch), seeds the sim from the header, and threads the replay through
  MainWindow to GameWorldView.
- GameWorldView: drives the player in onFrame (manual speed/pause kept,
  forward-only), gates the schematic-choices and game-over polls, and draws a
  "REPLAY" tag plus a passive "Replay ended" / "Desync at tick N" overlay.
- computeReplayConfigHash factored out of ReplayRecorder for reuse by main.

ReplayPlaybackTest records a scripted run, reads it back, replays it, and
asserts no desync + byte-identical final state -- including the
periodic-checksum-then-command ordering at a shared tick. Full suite green
(350 cases / 3396 assertions); app, tests, and balancing all build.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DUsFgd2Ga6pmLz8giS8WUn

src/ui/GameWorldView.h

@@ -41,6 +41,8 @@
 #include "VisualsConfig.h"
 
 struct Command;
+struct ParsedReplay;
+class ReplayPlayer;
 class Simulation;
 class QPainter;
 
@@ -68,7 +70,7 @@ class GameWorldView : public QOpenGLWidget,
 public:
     GameWorldView(Simulation* sim, const GameConfig* config,
                   const VisualsConfig* visuals, const std::string& configDir,
-                  QWidget* parent = nullptr);
+                  const ParsedReplay* replay, QWidget* parent = nullptr);
     ~GameWorldView() override;
 
     double gameSpeed() const;
@@ -121,6 +123,7 @@ private:
     void drawBeams(QPainter& painter);
     void drawOverlays(QPainter& painter);
     void drawScreenSpace(QPainter& painter);
+    void drawReplayOverlay(QPainter& painter);
 
     float    tilePx() const;
     float    viewportWidthTiles() const;
@@ -178,6 +181,9 @@ private:
     CommandManager m_commandManager;
     // A Reset command was enqueued; reset the view after the next drain applies it.
     bool           m_viewResetPending = false;
+    // Non-null => view-only playback: ticks are driven by the recorded stream and
+    // live input is ignored (the CommandManager is in replay mode).
+    std::unique_ptr<ReplayPlayer> m_replayPlayer;
 
     TickDriver    m_tickDriver;
     QElapsedTimer m_frameTimer;