對話可切全螢幕,亦可縮回側邊面板回到辦公室

摘要：
與 claude-office 同步:LIVE 對話新增全螢幕切換,展開為置中聊天卡片,
可用「回到辦公室」鈕或 Esc 縮回。

根本原因：
對話擠在側欄不利長對話閱讀。

影響：
純 UI 覆蓋層;側欄與全螢幕共用 ChatConversation,狀態同步。

修法：
抽出 ChatConversation(variant panel|full)、ChatFullscreen 覆蓋層、
store chatFullscreen 狀態、全螢幕毛玻璃版面。

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/styles.css

@@ -372,7 +372,88 @@
   cursor: default;
 }
 
-.chat-list {
+.chat-head-actions {
+  display: flex;
+  align-items: center;
+  gap: 12px;
+}
+
+.chat-head .link-btn:disabled {
+  opacity: 0.4;
+  cursor: default;
+}
+
+/* ── full-screen chat overlay ── */
+
+.chat-full-overlay {
+  position: fixed;
+  inset: 0;
+  z-index: 60;
+  background: color-mix(in srgb, var(--bg) 82%, transparent);
+  backdrop-filter: blur(6px);
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  padding: 24px;
+  animation: card-in 0.2s ease-out;
+}
+
+.chat-full-card {
+  width: min(860px, 100%);
+  height: min(88vh, 900px);
+  display: flex;
+  flex-direction: column;
+  background: var(--bg-panel);
+  border: 1px solid var(--border);
+  border-radius: 16px;
+  box-shadow: 0 20px 60px rgba(0, 0, 0, 0.35);
+  overflow: hidden;
+  padding: 18px 20px 20px;
+}
+
+.chat-full-topbar {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: 12px;
+  padding-bottom: 14px;
+  border-bottom: 1px solid var(--border);
+}
+
+.chat-full-who {
+  display: flex;
+  align-items: center;
+  gap: 12px;
+}
+
+.chat-full-who svg {
+  background: var(--bg-card);
+  border: 1px solid var(--border);
+  border-radius: 10px;
+  flex-shrink: 0;
+}
+
+.chat-full-who h2 {
+  font-family: "Sora", system-ui, sans-serif;
+  font-size: 20px;
+  font-weight: 600;
+  margin-bottom: 4px;
+}
+
+.chat-full-who .model-tag {
+  margin-left: 8px;
+}
+
+/* the shared conversation fills the full-screen card */
+.chat-panel-full {
+  flex: 1;
+  min-height: 0;
+  display: flex;
+  flex-direction: column;
+  margin-top: 14px;
+}
+
+.chat-panel-full .chat-list {
   display: flex;
   flex-direction: column;
   gap: 6px;