Type component children with a covariant Children alias

The builders annotated their ``children`` parameter as
``list[HTMLTag] | HTMLTag | None`` where ``HTMLTag = str``. ``list[str]`` is
invariant, so passing ``list[Element]`` / ``list[Node]`` — the normal case —
was a type error everywhere a component nested children.

Introduce a proper child type in core:

    Child    = Node | str
    Children = Sequence[Child] | str | None

``Sequence`` is covariant, so ``list[Element]`` / ``list[Node]`` are accepted;
``Child`` includes ``Node`` so node children are no longer rejected. ``Element``
itself also accepts a bare ``Node`` (it wraps one), typed ``Children | Node``.

Replace the ``list[HTMLTag] | HTMLTag | None`` annotations across primitives /
domain with ``Children``, and add ``as_children()`` to normalise a ``children``
argument to a ``list[Child]`` — retiring the repeated
``children if isinstance(children, list) else [children]`` dance that defeated
type narrowing. Inline ``mark_safe(...)`` SVG/markup children become ``Safe(...)``
nodes (a ``Node`` child instead of a stub-typed string).

Pyright on the component package drops from 43 to 22 errors; the remaining 22
are pre-existing and unrelated (django-stubs model access, the ``mark_safe``
``_Wrapped`` return type, and ``list[HTMLAttribute]`` attribute invariance).
Full suite green (443).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

common/components/domain.py

@@ -6,7 +6,7 @@ from django.template.defaultfilters import floatformat
 from django.urls import reverse
 from django.utils.safestring import SafeText, mark_safe
 
-from common.components.core import HTMLTag, Node
+from common.components.core import Children, Node, as_children
 from common.components.primitives import (
     A,
     Div,
@@ -21,13 +21,12 @@ from games.models import Game, Purchase, Session
 def GameLink(
     game_id: int,
     name: str = "",
-    children: list[HTMLTag] | HTMLTag | None = None,
+    children: Children = None,
 ) -> Node:
     """Link to a game's detail page. Uses children (slot) if provided, otherwise name."""
     from django.urls import reverse
 
-    children = children or []
-    display = children if children else [name]
+    display = as_children(children) or [name]
     link = reverse("games:view_game", args=[game_id])
 
     return Span(
@@ -38,7 +37,7 @@ def GameLink(
                 attributes=[
                     ("class", "underline decoration-slate-500 sm:decoration-2"),
                 ],
-                children=display if isinstance(display, list) else [display],
+                children=display,
             ),
         ],
     )
@@ -54,7 +53,7 @@ _STATUS_COLORS = {
 
 
 def GameStatus(
-    children: list[HTMLTag] | HTMLTag | None = None,
+    children: Children = None,
     status: str = "u",
     display: str = "",
     class_: str = "",
@@ -76,12 +75,12 @@ def GameStatus(
 
     return Span(
         attributes=[("class", outer_class)],
-        children=[dot] + (children if isinstance(children, list) else [children]),
+        children=[dot] + as_children(children),
     )
 
 
 def PriceConverted(
-    children: list[HTMLTag] | HTMLTag | None = None,
+    children: Children = None,
 ) -> Node:
     """Wrap content in a span that indicates the price was converted."""
     children = children or []
@@ -90,7 +89,7 @@ def PriceConverted(
             ("title", "Price is a result of conversion and rounding."),
             ("class", "decoration-dotted underline"),
         ],
-        children=children if isinstance(children, list) else [children],
+        children=as_children(children),
     )