refactor: extract the base styles and finish the aggregator (#266 slice 5/5)

52 блока host/переменных/кросс-поверхностных групп → src/styles/base.styles.ts;
styles.ts — 19-строчный сборщик [base, plan, devices, chrome, dialogs] с
задокументированным контрактом порядка каскада. Два оставшихся мутантных
якоря (:host-гейт ховера устройств) переадресованы на base.styles.ts.

Юниты инвариантов (test/styles-split.test.mjs): состав и порядок сборщика;
непересечение (scope+селектор) между файлами — единственное именованное
исключение: кросс-поверхностная группа «:host(...) .dev:hover, .dev:focus-
visible» живёт в base по §1.1; выживание медиа-обёрток — 2 forced-colors и
10 prefers-reduced-motion (в ТЗ и ревью фигурировали 8 — фактический счёт по
исходнику 10, юнит держит точное число). fix-test-build научился точке в
имени модуля (styles/base.styles → .js). ARCHITECTURE.md — раздел Styles.

Refactor-proof diff (scope-ключ) пуст; golden 129/129 без переприёмки; смоки
plan_snap_overlay/preloader OK; npm test 1318/0; бандл 1 291 440 → 1 291 458
(+18 байт).

Issue: #266
User-Visible: no

test/styles-split.test.mjs

@@ -0,0 +1,78 @@
+/** #266: invariants of the styles split. */
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { readFileSync } from 'node:fs';
+import { cardStyles, baseStyles, planStyles, devicesStyles, chromeStyles, dialogsStyles }
+  from '../test-build/styles.js';
+
+const FILES = ['base', 'plan', 'devices', 'chrome', 'dialogs'];
+const sourceOf = (name) =>
+  readFileSync(new URL(`../src/styles/${name}.styles.ts`, import.meta.url), 'utf8');
+
+const selectorsOf = (tsSource) => {
+  // Only the css`` payload: the TS import/export scaffolding is not CSS.
+  const css = [...tsSource.matchAll(/css`([\s\S]*?)`/g)].map((m) => m[1]).join('\n');
+  const text = css.replace(/\/\*[\s\S]*?\*\//g, '');
+  const out = new Set();
+  const walk = (chunk, scope) => {
+    let i = 0;
+    while (i < chunk.length) {
+      const open = chunk.indexOf('{', i);
+      if (open === -1) break;
+      const header = chunk.slice(i, open).replace(/\s+/g, ' ').trim();
+      let depth = 1, j = open + 1;
+      while (j < chunk.length && depth > 0) {
+        if (chunk[j] === '{') depth++;
+        else if (chunk[j] === '}') depth--;
+        j++;
+      }
+      if (header.startsWith('@media') || header.startsWith('@supports')) {
+        walk(chunk.slice(open + 1, j - 1), `${scope}${header} :: `);
+      } else if (!header.startsWith('@')) {
+        // The key includes the media scope: the SAME selector inside and
+        // outside a wrapper are different cascade entries by construction
+        // (a multi-zone @media block lands in base as a whole).
+        for (const sel of header.split(',')) out.add(`${scope}${sel.trim()}`);
+      }
+      i = j;
+    }
+  };
+  walk(text, '');
+  return out;
+};
+
+test('issue 266 the aggregator is exactly the five surface files in the cascade order', () => {
+  assert.deepEqual(cardStyles, [baseStyles, planStyles, devicesStyles, chromeStyles, dialogsStyles],
+    'the cascade order is a contract — the golden set was accepted against it');
+});
+
+test('issue 266 surface files do not share a single selector', () => {
+  const sets = FILES.map((name) => ({ name, set: selectorsOf(sourceOf(name)) }));
+  const clashes = [];
+  for (let i = 0; i < sets.length; i++) {
+    for (let j = i + 1; j < sets.length; j++) {
+      for (const sel of sets[i].set) {
+        if (sets[j].set.has(sel)) clashes.push(`${sel} (${sets[i].name} ∩ ${sets[j].name})`);
+      }
+    }
+  }
+  // Spec §1.3.2: every allowed exception is named with its reason.
+  const allowed = [
+    // The `:host([data-pointer-hover]) .dev:hover, .dev:focus-visible` GROUP
+    // is cross-surface (host gate + device selector) and therefore lives in
+    // base per spec §1.1, while the plain `.dev:focus-visible` outline rule
+    // stays with its surface. Their source order (group first, outline
+    // second) is preserved by the [base, …, devices] assembly order — golden
+    // holds the cascade.
+    '.dev:focus-visible (base ∩ devices)',
+  ];
+  assert.deepEqual(clashes, allowed);
+});
+
+test('issue 266 the media wrappers survived the move', () => {
+  const all = FILES.map((name) => sourceOf(name)).join('\n');
+  assert.equal((all.match(/@media \(forced-colors: active\)/g) || []).length, 2,
+    'both forced-colors blocks must survive — golden never emulates them');
+  assert.equal((all.match(/@media \(prefers-reduced-motion: reduce\)/g) || []).length, 10,
+    'all ten reduced-motion blocks must survive — golden always shoots reduced');
+});