Make component return types honest; drop str/mark_safe leftovers

Cleanup of hacky leftovers from the node-tree migration (no behaviour
change):

- Return annotations: the component builders return Node subtrees, not
  SafeText strings, but ~40 functions still declared `-> SafeText`. Correct
  them to `-> Node` across filters / search_select / date_range_picker /
  domain. The genuine string returners keep `-> SafeText`: the Alpine
  selectors (GameStatusSelector / SessionDeviceSelector, which build f-string
  markup) and the script-tag helpers (CsrfInput / ModuleScript /
  ExternalScript / StaticScript).
- layout.render_page / layout.Page / AddForm now accept `Node` in their
  `content` / `scripts` / `fields` parameters (TYPE_CHECKING import in
  layout to avoid the components import cycle), matching what views already
  pass.
- session._session_fields builds a `Fragment(*rows, separator="\n")` instead
  of `mark_safe("\n".join(str(row) ...))` — keeps the tree intact so media
  could bubble, per the Fragment convention.
- Inline SVG icon children use `Safe(...)` nodes instead of `mark_safe(...)`
  strings (filters mode-toggle + collapse icons, date_range_picker calendar
  icon).
- _filter_field reads the widget's own id from its node `.attributes`
  (`_widget_id`) for the label's `for`, dropping the superfluous `for_widget`
  argument that always rendered `for="None"`. Removes the two TODOs whose
  premise ("the Component function can't expose the id") the class/node
  refactor retired, plus RangeSlider's dead commented-out Label block.

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

common/components/primitives.py

@@ -622,8 +622,8 @@ def AddForm(
     form,
     *,
     request,
-    fields: SafeText | str | None = None,
-    additional_row: SafeText | str = "",
+    fields: Node | SafeText | str | None = None,
+    additional_row: Node | SafeText | str = "",
     submit_class: str = "mt-3",
 ) -> Node:
     """Page body for the generic add/edit form (Python equivalent of add.html).