v0.2 Phase 3: additive semantic tokens + KI-05 resolution

Additive token grammar (no renames, no replacements):

- --color-caution (dark #e8be4a, light #a08a1f) becomes the canonical
  name for tuned-amber notice surfaces in the new wrapper grammar
- --color-warning is kept as a CSS var() alias of --color-caution so
  every existing text-warning / bg-warning call site stays valid
- --color-info (dark #7a9ec0, light #3d6a8a) is the soft blue-grey
  signal for the new LumotiaNotice info variant
- --color-accent-environment (dark #8fae9a, light #4a7058) is an
  optional sage/moss support token for empty-state illustrations
  and environment-neutral status dots. NOT a brand swap — amber/
  copper --color-accent stays primary

Mirrored in src/design-system/colors_and_type.css (the buildless
preview pages bypass Tailwind so the duplication is intentional).

KI-05 resolved in the same commit, per the plan:

- src/lib/types/app.ts: drop `theme` from SettingsState
- src/lib/stores/page.svelte.ts: drop `theme: "Dark"` from defaults
- src/routes/+layout.svelte: drop the migration $effect, add a
  one-shot migrateLegacyTheme() on mount that copies any historical
  lumotia_settings.theme into preferences.theme and strips the
  legacy field. Idempotent — subsequent loads short-circuit
- src/routes/{float,viewer,preview}/+layout@.svelte: drop the same
  $effect; secondary windows inherit theme via PREFERENCES_CHANGED_EVENT
- src/lib/pages/SettingsPage.svelte: both SegmentedButton bindings
  (quick-settings row at :1272, Appearance group at :2606) now use
  Svelte 5 function bindings ({ get, set }) backed by prefs.theme
  and updatePreferences. No SegmentedButton API change

Phase 3 per-page gate green: npm run check (0/0/4129 files),
npm test (13/13), npm run test:e2e (16/16). No regressions in
the Phase 1 smoke baseline.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/routes/preview/+layout@.svelte

@@ -17,14 +17,8 @@
 
   const prefs = getPreferences();
 
-  // Keep transcript-editor theme sync trick: legacy settings → preferences
-  $effect(() => {
-    const legacyTheme = settings.theme;
-    const mapped = legacyTheme === "Light" ? "light" : legacyTheme === "Dark" ? "dark" : "system";
-    if (prefs.theme !== mapped) {
-      updatePreferences({ theme: mapped });
-    }
-  });
+  // v0.2 Phase 3 KI-05: theme is now preferences.theme only. The
+  // preview window inherits via PREFERENCES_CHANGED_EVENT below.
 
   if (typeof window !== "undefined") {
     window.addEventListener("storage", (event) => {