write(ui): 对话框填满 + 🎙/发送按钮浮在 textarea 框内右下

- input-row 改 position: relative + flex:1 撑满 input-bar 高度
- textarea width/height 100% 填满，右/下加 padding (130px / 14px) 给按钮腾位
- btn-tray absolute right:8 bottom:8，pointer-events: none 让 textarea 仍可点
- 按钮 height 40→32 更紧凑

apps/write/frontend/src/App.vue

@@ -340,18 +340,20 @@ onMounted(() => {
             :disabled="busy || activeId === null"
             @keydown="onInputKeydown"
           ></textarea>
-          <button
-            class="btn mic"
-            :class="{ on: recording }"
-            :disabled="busy || activeId === null"
-            @click="toggleMic"
-            :title="recording ? '停止录音' : '开始语音输入'"
-          >{{ recording ? '◼' : '🎙' }}</button>
-          <button
-            class="btn primary"
-            :disabled="busy || !inputText.trim() || activeId === null"
-            @click="sendMessage"
-          >发送</button>
+          <div class="btn-tray">
+            <button
+              class="btn mic"
+              :class="{ on: recording }"
+              :disabled="busy || activeId === null"
+              @click="toggleMic"
+              :title="recording ? '停止录音' : '开始语音输入'"
+            >{{ recording ? '◼' : '🎙' }}</button>
+            <button
+              class="btn primary"
+              :disabled="busy || !inputText.trim() || activeId === null"
+              @click="sendMessage"
+            >发送</button>
+          </div>
         </div>
         <div class="status" :class="{ err: statusErr }">{{ status }}</div>
       </div>

apps/write/frontend/src/styles.css

@@ -210,40 +210,61 @@ textarea, input { font: inherit; }
   background: var(--bg-elev);
   border-top: 1px solid var(--border-soft);
   padding: 10px 12px;
+  display: flex;
+  flex-direction: column;
+  min-height: 0;
+}
+.input-row {
+  flex: 1;
+  position: relative;
+  min-height: 0;
 }
-.input-row { display: flex; gap: 8px; align-items: flex-end; min-width: 0; }
 .input-row textarea {
-  flex: 1 1 0;
-  min-width: 0;
-  min-height: 40px;
-  max-height: 100%;
+  width: 100%;
+  height: 100%;
+  /* 右 + 下 padding 给悬浮按钮腾空间，文字不会爬到按钮下 */
+  padding: 11px 130px 14px 14px;
   resize: none;
-  padding: 9px 12px;
   border: 1px solid var(--border);
   background: var(--bg);
   color: var(--text);
-  border-radius: 8px;
+  border-radius: 10px;
   outline: none;
   font-size: 14px;
-  line-height: 1.4;
+  line-height: 1.5;
 }
 .input-row textarea::placeholder { color: var(--text-mute); }
 .input-row textarea:focus { border-color: var(--accent-strong); }
+.input-row textarea:disabled { opacity: 0.6; }
+
+/* 悬浮在 textarea 框线内右下 */
+.btn-tray {
+  position: absolute;
+  right: 8px;
+  bottom: 8px;
+  display: flex;
+  gap: 6px;
+  pointer-events: none;  /* 让 textarea 仍接受点击右下空白处定位光标 */
+}
+.btn-tray > * { pointer-events: auto; }
 
 .btn {
-  height: 40px;
+  height: 32px;
   padding: 0 14px;
-  border-radius: 8px;
+  border-radius: 7px;
   border: 1px solid var(--border);
   background: var(--bg-elev);
   color: var(--text-dim);
-  font-size: 14px;
+  font-size: 13px;
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
 }
 .btn:hover { background: var(--bg-hover); color: var(--text); }
-.btn.primary { background: var(--accent-strong); border-color: var(--accent-strong); color: #fff; }
+.btn.primary { background: var(--accent-strong); border-color: var(--accent-strong); color: #fff; font-weight: 600; }
 .btn.primary:hover { background: var(--accent); border-color: var(--accent); color: #fff; }
 .btn.primary:disabled { background: var(--bg-card); border-color: var(--border); color: var(--text-mute); cursor: not-allowed; }
-.btn.mic { width: 44px; padding: 0; }
+.btn.mic { width: 36px; padding: 0; }
 .btn.mic.on { background: var(--accent-red); border-color: var(--accent-red); color: #fff; }
 
 .status {