Own all form styling in components; remove form CSS from input.css

Form controls were styled "at a distance": Django renders bare
<input>/<select>/<textarea>/<label>, so input.css reached in with ID-scoped
#add-form descendant rules plus a global form *:disabled rule and .errorlist.
The #add-form ID specificity forced state rules to climb, needed
:not([data-search-select-search]) carve-outs, and broke on markup changes — it
surfaced as the add_purchase Name/related_game fields not reading as disabled.

Components now own all form styling via utilities on the elements themselves:

- PrimitiveWidgetsMixin stamps INPUT/SELECT/TEXTAREA_CLASS (incl. disabled:
  variants) onto native widgets by type, skipping SearchSelect (self-styled)
  and checkboxes.
- New FormFields(form, *, extras=...) renders label + control + errors + row
  layout with their own classes (replaces form.as_div()); the <form> owns its
  flex layout. extras appends a node into a named field's row (session
  timestamp buttons).
- AddForm/purchase/session render via FormFields; login too — a new
  LoginForm(PrimitiveWidgetsMixin, AuthenticationForm) styles its inputs and
  auth.py renders it via FormFields + a StyledButton (was as_table).
- input.css loses the entire #add-form block, the global :disabled rule, and
  .errorlist. State (disabled:) now lives on the element — no specificity wars,
  no carve-outs, robust to markup edits.

Tests: error rendering uses the component class (not .errorlist); add-form
labels/inputs carry their own classes; e2e login fixtures click the Login
button by text (submit is now a <button>); Name disabled cursor asserted.
CLAUDE.md documents the no-styling-at-a-distance + FormFields conventions.

513 passed; lint/format/ts-check clean.

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

games/views/purchase.py

@@ -22,6 +22,7 @@ from common.components import (
     CsrfInput,
     Div,
     Element,
+    FormFields,
     Fragment,
     GameLink,
     Icon,
@@ -32,7 +33,6 @@ from common.components import (
     Node,
     PriceConverted,
     PurchasePrice,
-    Safe,
     SelectionFields,
     StyledButton,
     TableRow,
@@ -296,7 +296,7 @@ def add_purchase(request: HttpRequest, game_id: int = 0) -> HttpResponse:
         AddForm(
             form,
             request=request,
-            fields=Fragment(Safe(form.as_div()), _pricing_controls()),
+            fields=Fragment(FormFields(form), _pricing_controls()),
             additional_row=_purchase_additional_row(),
         ),
         title="Add New Purchase",