feat(shell): MainWindowShell assembles the frame and wires the DM loop

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

client/tests/unit/test_main_window_shell.gd

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+extends "res://addons/gut/test.gd"
+
+const SCENE := "res://scenes/shell/MainWindowShell.tscn"
+const FakeTransport = preload("res://tests/doubles/fake_transport.gd")
+const DmResponse = preload("res://scripts/net/dm_response.gd")
+
+
+func _shell() -> MainWindowShell:
+	# Inject a fake service BEFORE _ready (add_child) so the initial narrate does
+	# not touch the network — instantiate() does not run _ready(); add_child does.
+	var node = load(SCENE).instantiate()
+	var transport = FakeTransport.new()
+	transport.set_response(DmResponse.ok(200, {"prose": "Rain on the cobbles."}))
+	node.service = DmService.new(transport, FallbackLibrary.new())
+	add_child_autofree(node)
+	return node
+
+
+func test_shell_applies_theme_and_fits_viewport():
+	var packed = load(SCENE)
+	assert_true(packed is PackedScene)
+	var node := _shell()
+	assert_true(node is Control)
+	assert_true(node.theme is Theme, "shell applies game_theme")
+	assert_gt(node.size.x, 0.0, "viewport-fit sized the root (M3-a collapse guard)")
+
+
+func test_shell_mounts_both_panels():
+	var node := _shell()
+	assert_not_null(node.book, "narration book mounted")
+	assert_not_null(node.dock, "system dock mounted")
+
+
+func test_shell_builds_a_code_owned_seed_log():
+	var node := _shell()
+	assert_not_null(node._log, "a canon log exists to post (§11)")
+	assert_gt(node._log.established_facts.size(), 0, "seed scene facts are code-owned")

client/tests/unit/test_main_window_shell.gd.uid

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+uid://dbd4cq1awo4su