feat(ui): Skills tab stub content (Workstream 8, #618)

Replaces the W5 placeholder inside the Skills tab with a properly
framed stub per Araminta's spec. Final workstream of the #618 + #680
+ MetaScreen implementation.

Content:
- MarginContainer (8 px sides, 4 px top — matches existing tab
  padding)
- Single centered Label: "Skills allocation — coming soon."
- DIM_TEXT color, font_body size (11 px), horizontally and vertically
  centered inside the tab content area

No inputs, no interactivity — real skill allocation lands in a future
sprint when the skills system exists server-side. Players selecting
a bookmark still proceed to Start regardless of what they see on this
tab.

Closes the implementation half of #618 (CK3-style character creation
screen) and #680 (location picker) — Hoshe's revised test plans for
MetaScreen pattern, #618, and #680 can now run end-to-end.

Verification:
- gdlint clean
- Headless parse + widened scanner check (per hardened pr-push skill)
  clean; pre-existing autoload class_name noise filtered.
- test_character_creation_sprint28 88/88, test_protocol 62/62,
  test_client_p3 24/24, test_ui_framework_sprint15 54/54

Next: Hoshe runs her full revised test gauntlet against the shipped
shape; if green, the PR pushes via /pr-push.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

client/ui/meta/screens/character_creation/character_creation.gd

@@ -606,15 +606,22 @@ func _update_appearance_sub_btns() -> void:
 
 
 func _build_skills_tab(tab: Control) -> void:
+	var margin := MarginContainer.new()
+	margin.set_anchors_and_offsets_preset(Control.PRESET_FULL_RECT)
+	margin.add_theme_constant_override("margin_left", 8)
+	margin.add_theme_constant_override("margin_right", 8)
+	margin.add_theme_constant_override("margin_top", 4)
+	tab.add_child(margin)
+
 	var lbl := Label.new()
-	lbl.text = "Skills content lands in Workstream 8."
+	lbl.text = "Skills allocation — coming soon."
 	lbl.add_theme_color_override("font_color", TEXT_DIM)
-	lbl.add_theme_font_size_override("font_size", 12)
+	lbl.add_theme_font_size_override("font_size", 11)
 	lbl.horizontal_alignment = HORIZONTAL_ALIGNMENT_CENTER
 	lbl.vertical_alignment = VERTICAL_ALIGNMENT_CENTER
 	lbl.set_anchors_and_offsets_preset(Control.PRESET_FULL_RECT)
 	lbl.mouse_filter = Control.MOUSE_FILTER_IGNORE
-	tab.add_child(lbl)
+	margin.add_child(lbl)
 
 
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