Add save migration fixtures and failure-mode coverage

src/test/fixtures/saves/campaign_0_8.json

@@ -0,0 +1,11 @@
+{
+	"index": 1,
+	"next_venue": "joke_shop",
+	"shift_number": 2,
+	"difficulty": "hard",
+	"complete": false,
+	"completed": [
+		"hollywood_building"
+	],
+	"last_grade": "B"
+}

src/test/fixtures/saves/settings_0_8.json

@@ -0,0 +1,15 @@
+{
+	"look_sensitivity": 0.0031,
+	"hud_font_scale": 1.15,
+	"invert_y": true,
+	"head_bob": false,
+	"input_bindings": {
+		"inspect": {
+			"type": "key",
+			"code": 90
+		}
+	},
+	"ai_difficulty": "hard",
+	"tutorial_completed": true,
+	"tutorial_skipped": false
+}

src/test/fixtures/saves/shift_results_0_8.json

@@ -0,0 +1,20 @@
+[
+	{
+		"scenario_id": "hollywood_building",
+		"reputation": {
+			"rating": 81.0,
+			"grade": "B"
+		},
+		"spawned_count": 6,
+		"completed_at_ms": 1000
+	},
+	{
+		"scenario_id": "joke_shop",
+		"reputation": {
+			"rating": 74.5,
+			"grade": "C"
+		},
+		"spawned_count": 5,
+		"completed_at_ms": 2000
+	}
+]

src/test/fixtures/saves/shift_state_0_9_0.json

@@ -0,0 +1,26 @@
+{
+	"version": 1,
+	"scenario_id": "joke_shop",
+	"guard_position": [0.0, 0.1, 10.5],
+	"guard_yaw": 1.25,
+	"head_pitch": 0.1,
+	"door_locked": true,
+	"flashlight_on": true,
+	"body_camera_on": true,
+	"npc_counter": 7,
+	"coordinator": {
+		"duration_s": 900.0,
+		"elapsed_s": 540.0,
+		"current_phase": 3,
+		"phase_offset_s": 700.0,
+		"spawned_count": 7,
+		"responder_outcomes": [],
+		"investigations": [],
+		"recorder": {},
+		"reputation": {},
+		"crowd": {},
+		"radio": {},
+		"scheduler": {}
+	},
+	"npcs": []
+}