feat(engine): live server visual tests and gauntlet snapshot replay

Add live server lifecycle to tests/run-visual (start/stop server per
scenario, parse LISTENING:{port}). Add MessagePack snapshot replay to
visual_capture.gd via Protocol.decode_snapshot() — exercises the full
client pipeline from wire bytes to rendered fog. Three replay scenarios
(hub_spawn, fog_theater, hub_after_movement) plus one live scenario
(fog_live_hub). Add gen_gauntlet_fixtures.rs to produce .msgpack fixtures
from the Gauntlet test world. Add max_diff_pct threshold to visual-diff.
Makefile: add fixtures-gauntlet target, fix build-client double-import,
preserve .godot cache in clean.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/visual.json

@@ -2,6 +2,7 @@
   "resolution": [960, 540],
   "settle_frames": 30,
   "tolerance": 5,
+  "max_diff_pct": 0.5,
   "golden_dir": "client/tests/golden/visual",
   "scenarios": {
     "fog_3state": {
@@ -47,6 +48,26 @@
     "cursor_menu": {
       "ticks": 3,
       "description": "Cursor rendering over dialogue option"
+    },
+    "fog_live_replay": {
+      "ticks": 1,
+      "description": "Replay real server hub snapshot — full pipeline fog test",
+      "replay_snapshot": "tests/fixtures/gauntlet/hub_spawn.msgpack"
+    },
+    "fog_theater_replay": {
+      "ticks": 1,
+      "description": "Replay Fog Theater — large room with NPCs at varying distances",
+      "replay_snapshot": "tests/fixtures/gauntlet/fog_theater.msgpack"
+    },
+    "fog_boundary_replay": {
+      "ticks": 1,
+      "description": "Replay hub after movement — explored/visible tile boundary",
+      "replay_snapshot": "tests/fixtures/gauntlet/hub_after_movement.msgpack"
+    },
+    "fog_live_hub": {
+      "ticks": 10,
+      "live": true,
+      "description": "Live server: Hub spawn fog — real pipeline regression test"
     }
   },
   "flows": {