refactor(shell): author shell scenes as editor-previewable node trees

Move the three shell scenes (SystemDock, NarrationBook, MainWindowShell)
from build-everything-in-_ready() to authored .tscn node trees with the
theme + type-variations set in the editor, so the layout previews and can
be arranged in the Godot editor. Scripts keep only on-load work: @onready
node refs, DM-loop wiring, the dock slide, and binding seed ShellState into
the fixed authored turn-order tokens + consumable slots.

Fixes the dock offset + over-long buttons (now fixed-width DockButtons in a
right-anchored menu). Headless probe: root 1920x1080, world/book split
1180/740, dock at the world's right edge — no collapse. Suite 138/138.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

client/scenes/shell/SystemDock.tscn

@@ -1,6 +1,86 @@
-[gd_scene load_steps=2 format=3]
+[gd_scene load_steps=3 format=3]
 
 [ext_resource type="Script" path="res://scripts/ui/shell/system_dock.gd" id="1"]
+[ext_resource type="Theme" path="res://assets/theme/game_theme.tres" id="2"]
 
 [node name="SystemDock" type="Control"]
+layout_mode = 3
+anchors_preset = 0
+offset_right = 240.0
+offset_bottom = 420.0
+theme = ExtResource("2")
 script = ExtResource("1")
+
+[node name="Menu" type="VBoxContainer" parent="."]
+layout_mode = 1
+anchor_left = 1.0
+anchor_right = 1.0
+offset_left = -190.0
+offset_right = -10.0
+offset_bottom = 316.0
+grow_horizontal = 0
+theme_override_constants/separation = 10
+
+[node name="Inventory" type="Button" parent="Menu"]
+custom_minimum_size = Vector2(0, 42)
+layout_mode = 2
+theme_type_variation = &"DockButton"
+text = "I   Inventory"
+alignment = 0
+metadata/screen_id = &"inventory"
+
+[node name="Character" type="Button" parent="Menu"]
+custom_minimum_size = Vector2(0, 42)
+layout_mode = 2
+theme_type_variation = &"DockButton"
+text = "C   Character"
+alignment = 0
+metadata/screen_id = &"character"
+
+[node name="QuestLog" type="Button" parent="Menu"]
+custom_minimum_size = Vector2(0, 42)
+layout_mode = 2
+theme_type_variation = &"DockButton"
+text = "J   Quest Log"
+alignment = 0
+metadata/screen_id = &"quest_log"
+
+[node name="Spellbook" type="Button" parent="Menu"]
+custom_minimum_size = Vector2(0, 42)
+layout_mode = 2
+theme_type_variation = &"DockButton"
+text = "K   Spellbook"
+alignment = 0
+metadata/screen_id = &"spellbook"
+
+[node name="WorldMap" type="Button" parent="Menu"]
+custom_minimum_size = Vector2(0, 42)
+layout_mode = 2
+theme_type_variation = &"DockButton"
+text = "M   World Map"
+alignment = 0
+metadata/screen_id = &"world_map"
+
+[node name="Party" type="Button" parent="Menu"]
+custom_minimum_size = Vector2(0, 42)
+layout_mode = 2
+theme_type_variation = &"DockButton"
+text = "P   Party"
+alignment = 0
+metadata/screen_id = &"party"
+
+[node name="Handle" type="Button" parent="."]
+custom_minimum_size = Vector2(26, 104)
+layout_mode = 1
+anchor_left = 1.0
+anchor_top = 0.5
+anchor_right = 1.0
+anchor_bottom = 0.5
+offset_left = -222.0
+offset_top = -52.0
+offset_right = -196.0
+offset_bottom = 52.0
+grow_horizontal = 0
+grow_vertical = 2
+theme_type_variation = &"TabActive"
+text = "›"