M6.3: Trait popovers — shared PopoverLayer + TraitChip triggers

Per GODOT_PORTING_GUIDE.md §6 (and §12 build order — popovers before
the easy card-grid steps because traits/skills/bonuses surface them
everywhere). One reusable popover panel; lightweight chip triggers.

Scenes/Widgets/PopoverLayer.cs:
  CanvasLayer added once as a child of Wizard.tscn. Owns one
  PanelContainer + close Timer; static Instance for chip-side access.
  ShowFor(trigger, ...) populates and positions the popover at the
  trigger's global rect with viewport clamp + flip-above logic
  (mirrors src/trait-hint.jsx). 80 ms grace period when moving from
  trigger to popover so the popover stays open across the gap.
  Detriment popovers get a red Modulate as a placeholder for the
  seal-coloured StyleBox the theming pass will install.

Scenes/Widgets/TraitChip.cs:
  Lightweight PanelContainer + Label trigger. On MouseEntered asks
  PopoverLayer.Instance to show; on MouseExited schedules close.
  Pill styling deferred to theming (default Godot panel for now;
  TraitChip / TraitChipDetriment styleboxes will land alongside
  the parchment Theme pass).

Wizard.tscn:
  PopoverLayer added as a top-level CanvasLayer child so popovers
  float above every step's content regardless of where the trigger
  is in the tree.

Steps/StepClade.cs:
  Replaces the placeholder "{n} traits, {m} detriments" line with an
  HFlowContainer of TraitChip per trait + per detriment. Hover any
  chip → popover shows name + description (+ DETRIMENT tag for the
  detriment chips).

  Also: cards switched from Button to PanelContainer for content-
  driven height. Button isn't a Container, so its intrinsic min
  size didn't aggregate from the inner vbox — at higher trait
  counts the chips overflowed into the cards below. PanelContainer
  is a Container, so the card grows with its content. GuiInput
  handles the click-to-select; selected state shown via Modulate
  tint until the proper StyleBox swap lands in theming.

Closes M6.3. Per guide §12, next is M6.4 — easy card-grid steps
(Species / Calling / Subclass / History) variations on the StepClade
pattern, then StepSkills, then StepReview.

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

Theriapolis.Godot/Scenes/Wizard.tscn

@@ -1,8 +1,9 @@
-[gd_scene load_steps=4 format=3 uid="uid://wizard6m6v1"]
+[gd_scene load_steps=5 format=3 uid="uid://wizard6m6v1"]
 
 [ext_resource type="Script" path="res://Scenes/Wizard.cs" id="1_wizard"]
 [ext_resource type="Script" path="res://UI/Widgets/CodexStepper.cs" id="2_stepper"]
 [ext_resource type="PackedScene" path="res://Scenes/Aside.tscn" id="3_aside"]
+[ext_resource type="Script" path="res://Scenes/Widgets/PopoverLayer.cs" id="4_popover"]
 
 [node name="Wizard" type="Control"]
 anchors_preset = 15
@@ -85,3 +86,6 @@ text = "1 / 8"
 [node name="NextButton" type="Button" parent="Wrap/Layout/NavBar"]
 unique_name_in_owner = true
 text = "Next ›"
+
+[node name="PopoverLayer" type="CanvasLayer" parent="."]
+script = ExtResource("4_popover")