fix(frontend): restore Ref document and control contracts

Ref's `.bg0/.bg1/.bg2` set only a background image and `html, body` centre the
texture with vertical tiling, so the extra background colours and the default
tiling are removed. Two ranking views declared unscoped `body` rules that leaked
a 500px min-width and a 21px line-height onto every screen; each page now owns
its own contract. Controls that Ref renders with the Bootstrap/Lumen family get
the shared modifier so the bottom edge moves on hover and while pressed.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

app/game-frontend/src/views/DiplomacyView.vue

@@ -271,7 +271,7 @@ onBeforeUnmount(() => {
             <tbody>
                 <tr>
                     <td>
-                        외 교 부<br /><button class="legacy-button" type="button" @click="router.push('/')">
+                        외 교 부<br /><button class="legacy-button legacy-button--primary" type="button" @click="router.push('/')">
                             돌아가기
                         </button>
                     </td>
@@ -622,7 +622,7 @@ onBeforeUnmount(() => {
             <tbody>
                 <tr>
                     <td>
-                        <button class="legacy-button" type="button" @click="router.push('/')">돌아가기</button
+                        <button class="legacy-button legacy-button--primary" type="button" @click="router.push('/')">돌아가기</button
                         ><br /><br />
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