M6.20: TitleScreen entry point with parchment-themed button stack

Default boot now lands on a centered title screen instead of the M0
hello-world label. Vertical button stack — New Character, Continue,
Quit — over the codex parchment field, with the H1 codex title and a
PORT / GODOT · M6.20 version chip in the bottom-right.

Continue is disabled until user://character.json exists; clicking it
prints a placeholder until the M7 play loop can pick the persisted
state up. New Character swaps the title for the wizard scene under
the Main parent. The wizard's existing "← Title" back-button on
Step 0 now actually does something — TitleScreen wires its
BackToTitle signal to a parent-side swap that reinstates the title
screen when the player backs out.

--wizard command-line flag still skips straight to the wizard for
fast-path development. Layout uses SetAnchorsAndOffsetsPreset
(LayoutPreset.FullRect) on the backing panel and CenterContainer —
manual AnchorRight = 1 doesn't fill in code because Godot's anchor
setters preserve visual position by adjusting offsets, leaving the
control at 0×0.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Theriapolis.Godot/Main.tscn

@@ -7,17 +7,3 @@ anchors_preset = 15
 anchor_right = 1.0
 anchor_bottom = 1.0
 script = ExtResource("1_main")
-
-[node name="Label" type="Label" parent="."]
-anchors_preset = 8
-anchor_left = 0.5
-anchor_top = 0.5
-anchor_right = 0.5
-anchor_bottom = 0.5
-offset_left = -200.0
-offset_top = -16.0
-offset_right = 200.0
-offset_bottom = 16.0
-horizontal_alignment = 1
-vertical_alignment = 1
-text = "Theriapolis · Godot port · M0 · F11 toggles fullscreen"