Ban SafeText-as-child: only Safe nodes render unescaped

Tightens the child model so the type is honest end to end. Previously a
``SafeText``/``mark_safe`` string passed as a child rendered unescaped — a
trusted-HTML-as-string backdoor that ``Child = Node | str`` couldn't express
(every ``SafeText`` is a ``str``). Now ``_child_key`` escapes *every* string
child; the only way to put trusted pre-rendered HTML into the tree is a
``Safe`` node. So a ``str`` child is always untrusted text — which is exactly
what the renderer escapes.

Converted the trusted-HTML children that relied on the old passthrough:

- ``CsrfInput`` and the Alpine selectors (``GameStatusSelector`` /
  ``SessionDeviceSelector``) now return ``Safe`` nodes instead of ``mark_safe``
  strings — they are always tree children.
- ``popover_content`` is now a ``Child`` (it is rendered as a child); the one
  HTML caller (``LinkedPurchase``) passes ``Safe(...)``.
- View-side children that were ``mark_safe`` strings → ``Safe(...)``:
  ``_played_row`` (game detail), the stat SVGs and `` `` spacer (game),
  the login table (auth), the manual session-form field/label markup
  (session), and ``_purchase_name`` (stats).
- ``SimpleTable.header_action`` typed ``Child``.

The script-tag string helpers (``ModuleScript`` / ``StaticScript`` /
``ExternalScript``) stay ``SafeText`` strings: they are only ever joined into
the ``scripts=`` string, never used as tree children.

``Children`` regains a bare ``Node`` member (a single node child is valid);
the one ``*children`` site (``Popover``) normalises via ``as_children`` first.
Tests that asserted the old SafeText-passthrough now assert the new rule
(mark_safe child escaped; ``Safe`` node passes through). Full suite green
(445; +2 new escaping tests).

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

games/views/session.py

@@ -22,6 +22,7 @@ from common.components import (
     NameWithIcon,
     Node,
     Popover,
+    Safe,
     SearchField,
     SessionDeviceSelector,
     paginated_table_content,
@@ -199,9 +200,9 @@ def _session_fields(form) -> Fragment:
     """
     rows: list[Node] = []
     for field in form:
-        children: list[SafeText | str] = [
-            mark_safe(str(field.label_tag())),
-            mark_safe(str(field)),
+        children: list[Node | str] = [
+            Safe(str(field.label_tag())),
+            Safe(str(field)),
         ]
         if field.name in ("timestamp_start", "timestamp_end"):
             this_side = "start" if field.name == "timestamp_start" else "end"