feat(ui): one high-voltage theme, and pick your character from the escape menu

The theme was a comic one — cream paper, ink borders, papaya. It is now a
charged one: near-black violet, hot papaya, and a lightning yellow spent
nowhere except the instant a button is pressed. Chips are cut with two sharp
corners and two round ones on a diagonal, which is as close to a skew as a
StyleBoxFlat gets and is the difference between a button that reads calm and
one that reads fast. BoltRule draws the motif itself, struck a third of the way
along its rule rather than centred, so it reads as something that HIT the line.

The pause menu was 900 lines of hand-rolled UI that never referenced UITheme at
all, so it rendered in Godot's default grey. It now applies the theme — and
applies it to its own root Control, not only to the Window, because a Control
inherits from its nearest Control ANCESTOR and this screen hangs off a
CanvasLayer, which is not one. That was invisible at first: the parts built with
UITheme.title() carry their own overrides and looked right next to a list and a
button that did not.

And it now has a Character screen. The roster on the left, the character
themselves on the right, turning — a name in a dropdown is not a character
selection screen. The preview is a real SkinnedPlayerModel in its own world, so
it shows exactly what will spawn: the same cel look, the same per-class
outlines, the same cloth and hair on springs. Selecting applies immediately;
there is nothing destructive to confirm, and applying on selection means the
character behind the menu changes as you arrow the list, which IS the
comparison.

PlayerMovementController.set_skin() is the supported way in. Both halves of a
skin change are easy to do by halves — `synced_skin_id` is what REMOTE peers
rebuild from, and only their _process watches it, so setting the property alone
would change everyone else's view of you and not your own.

Checked rather than asserted. debug/character_picker_check.gd walks the whole
roster and proves each entry loads a skeleton, animations, a surface table and
body surfaces — and that the skeleton is MOVING, because the clip name is a
variable this class sets on itself and reads "Idle" just as happily when nothing
is ticking. debug/ui_capture.gd and debug/roster_capture.gd photograph the
screens and every character, which is how three things were found that no
assertion could see: the theme break above, a preview showing the back of the
character's head, and a turntable that carried on from the last character so the
third one you looked at was side-on.

Known and not fixed here: momo's idle pose is wrong — arms overhead and a
pinched waist. Her rig, not the picker; every other character is correct.

Co-Authored-By: Claude Opus 5 <[email protected]>

debug/weapon_lab.tscn

@@ -1,4 +1,4 @@
-[gd_scene load_steps=2 format=3 uid="uid://cwpnlabweapon01"]
+[gd_scene format=3 uid="uid://c1aec1m0pwuk3"]
 
 [ext_resource type="Script" path="res://debug/weapon_lab.gd" id="1_lab"]