feat(conversation): cheap-default DeepSeek + Enter-send + model pill

- default-interactive@1 model: claude-haiku-4-5 → deepseek/deepseek-chat
  (input $0.28/$1.12 per 1M; haiku 대비 ~75% 절감).  fallback 은 haiku 로 swap.
- conversation textarea keydown:
  - Enter → 전송 (IME composition 중이면 무시)
  - Shift+Enter → 줄바꿈
  - Cmd/Ctrl+Enter → 전송 (백워드 호환)
  - Placeholder 안내 갱신.
- conversation top-bar 에 model pill 추가 (#session-model-pill) — 현재 세션의
  활성 model 을 monospace badge 로 표시.  헷갈리던 "어느 모델인가?" 해소.
- style.css 에 .conv-model-pill (회색 pill).

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

my-deepagent/static/app.js

@@ -757,6 +757,21 @@ function updateSessionStatePill(state) {
   pill.className = `conv-session-state state-${state}`;
 }
 
+function updateSessionModelPill(model) {
+  const pill = $conv("#session-model-pill");
+  if (!pill) return;
+  if (!model) {
+    pill.textContent = "";
+    pill.className = "conv-model-pill";
+    return;
+  }
+  // Trim the "openrouter:" prefix for display; keep full id in tooltip.
+  const display = model.replace(/^openrouter:/, "");
+  pill.textContent = display;
+  pill.title = `model: ${model}`;
+  pill.className = "conv-model-pill";
+}
+
 async function loadSessionList() {
   try {
     const list = await jsonFetch("/sessions?limit=50");
@@ -797,6 +812,7 @@ async function loadAndAttachSession(sessionId) {
     return;
   }
   updateSessionStatePill(detail.session.state);
+  updateSessionModelPill(detail.session.model);
 
   const messages = detail.messages || [];
   for (const m of messages) {
@@ -968,17 +984,14 @@ async function bootstrapConversationPage() {
     setTimeout(() => { input._composing = false; }, 0);
   });
   input.addEventListener("keydown", (ev) => {
-    // Honor Cmd/Ctrl+Enter as explicit "send" override even during composition.
-    if ((ev.metaKey || ev.ctrlKey) && ev.key === "Enter") {
-      ev.preventDefault();
-      sendMessage(ev.target.value);
-      return;
-    }
-    // Plain Enter during composition (e.g. Korean IME committing 한글) must
-    // pass through to the textarea — do nothing.
-    if (ev.key === "Enter" && input._composing) {
-      return;
-    }
+    if (ev.key !== "Enter") return;
+    // Shift+Enter → newline (let the textarea handle it natively).
+    if (ev.shiftKey) return;
+    // IME composition (Korean/Japanese/Chinese candidate commit) → never send.
+    if (input._composing) return;
+    // Plain Enter (and Cmd/Ctrl+Enter for backwards compat) → send.
+    ev.preventDefault();
+    sendMessage(ev.target.value);
   });
   // v0.3 PR #8: deep link `?session=<id>` auto-loads the named session.
   const params = new URLSearchParams(window.location.search);