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/lib/sim/ReplayRecorder.h

@@ -8,6 +8,10 @@
 
 struct Command;
 
+// 64-bit hash (16-char hex) over the *.toml files in configDir. Stored in the
+// replay header and recomputed on playback to detect a config mismatch.
+std::string computeReplayConfigHash(const std::string& configDir);
+
 // Writes a replay file as the game runs (see docs/replay_design.md). The format
 // is line-oriented append-friendly text: a small keyed header, then one line per
 // command (tick-tagged) interleaved with RNG-state checksum lines for desync
@@ -43,9 +47,6 @@ public:
     const std::string& currentFilePath() const;
 
 private:
-    // 64-bit hash over the *.toml files in m_configDir, as a 16-char hex string.
-    std::string computeConfigHash() const;
-
     std::string   m_configDir;
     std::string   m_outputDir;
     std::string   m_filePath;