Add the foundation stylesheet, written without Tailwind

Plan step 33. foundation.css is the one required import: the full
material layer statement, then plain imports of its parts, each opening
with the same statement.

- foundation/reset.css (material.reset): Tailwind 4's preflight rule for
  rule, with M3's on-surface-variant placeholder and no typeface.
- foundation/hidden.css: [hidden] and [x-cloak], outside every layer.
- foundation/tokens.css (material.tokens): the token files.
- foundation/base.css (material.base): the page's surface, ink and
  brand typeface, and the font face.
- foundation/interaction.css (material.base): md-state-layer,
  md-focus-ring, md-touch-target and md-link, the plain-CSS forms of the
  utilities; md-state-layer also takes data-md-dragged, and
  md-touch-target is 48px (space600) where the utility reads 3rem.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qwx5USif3wFFmxtHg5U1g9

resources/css/foundation/base.css

@@ -0,0 +1,24 @@
+/*
+ * The page itself: M3's background and default ink, in the brand typeface.
+ *
+ * The page is `surface` and its text `on-surface`, the default typography colour
+ * (docs/reference/m3/styles.md § Typography, "Accessibility requirements"). `color-scheme` is
+ * declared with the roles in tokens/scheme.css, so native controls and scrollbars change with
+ * `data-theme` in the same block as the colours. The typeface is
+ * `--md-ref-typeface-brand` (tokens/type.css), Google Sans Flex from tokens/font.css, whose
+ * `@font-face` this file imports into the same layer.
+ *
+ * In `material.base`, above the reset and below every component and text class.
+ */
+
+@layer material.reset, material.tokens, material.base, material.layout, material.components, material.text, material.visibility;
+
+@import '../tokens/font.css';
+
+@layer material.base {
+    html {
+        background-color: var(--md-sys-color-surface);
+        color: var(--md-sys-color-on-surface);
+        font-family: var(--md-ref-typeface-brand);
+    }
+}