replay: record every run to a replay file (Phase 2)

Hooks a recorder into the command chokepoint so each run is written to disk as
it plays, ready for playback in Phase 3.

- ReplayRecorder (lib): line-oriented append-friendly file — keyed header
  (version, build, seed, config_hash, timestamp), then '---', then tick-tagged
  command lines interleaved with "# checksum <tick> <hex>" RNG fingerprints.
  Each line is flushed so a crash leaves a valid partial file. Config hash is a
  64-bit FNV over the config dir's *.toml files; build tag is __DATE__/__TIME__.
- CommandSerializer (lib): per-command text (length-prefixed variable parts;
  ship layouts and splitter filters serialized inline). Reset is a file
  boundary, never a stream entry.
- CommandManager owns an optional ReplayRecorder: drain() records each applied
  command + a post-apply checksum; a drained Reset rolls to a new file;
  recordTickCheckpoint() (called per tick from onFrame) writes a checksum every
  30 ticks.
- Random seed generated in main and on restart (std::random_device); Simulation
  retains it via getSeed() for the header.
- GameWorldView attaches the recorder at construction (first file + tick-0
  checksum); replays land in <data>/replays named <timestamp>_<seed>.replay.

ReplayRecorderTest covers serialization, file well-formedness, file rolling,
and the CommandManager drain->record integration. Full suite green
(346 cases / 3377 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/CommandSerializer.h

@@ -0,0 +1,15 @@
+#pragma once
+
+#include <string>
+
+struct Command;
+
+// Serializes a command to a single-line, space-delimited token sequence for the
+// replay file (see docs/replay_design.md "File format: line-oriented ...").
+// Config ids (building types, recipes, items, modules) are whitespace-free
+// identifiers, so space delimiting is unambiguous; variable-length parts are
+// length-prefixed so the matching parser (added in Phase 3) is unambiguous.
+//
+// Reset is a file boundary (it rolls the replay file), not a stream entry, so it
+// is never serialized here.
+std::string serializeCommand(const Command& command);