feat: behind-the-scenes 👍/👎 rating system (fine-tune data collection)

Brian can rate Lyra's outputs as he uses her; each rating is stored as a
(context, content, rating) triple — the shape a future fine-tune / preference
dataset wants, collected passively during real use.

- memory: ratings table + add_rating (upsert: one row per item, re-rating
  replaces), list_ratings, rating_counts
- server: POST /rate, GET /ratings/counts, GET /ratings/export (JSONL download)
- chat UI: subtle 👍/👎 on each assistant reply, captures the prompting message
  as context
- journal/reflection UI: 👍/👎 on each thought
- tests: counts + upsert-replace behavior

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lyra/web/static/index.html

@@ -354,12 +354,46 @@
     return out.join("\n");
   }
 
+	function addRateBar(div) {
+	  const bar = document.createElement("div");
+	  bar.className = "rate-bar";
+	  const up = document.createElement("button");
+	  up.className = "rate-btn"; up.textContent = "👍"; up.title = "Good — more like this";
+	  const down = document.createElement("button");
+	  down.className = "rate-btn"; down.textContent = "👎"; down.title = "Off — less like this";
+	  up.addEventListener("click", () => rateMessage(div, 1, up, down));
+	  down.addEventListener("click", () => rateMessage(div, -1, up, down));
+	  bar.appendChild(up); bar.appendChild(down);
+	  div.appendChild(bar);
+	}
+
+	function rateMessage(div, value, up, down) {
+	  // context = the nearest preceding user message
+	  let ctx = "", p = div.previousElementSibling;
+	  while (p) {
+	    if (p.classList && p.classList.contains("user")) { ctx = p.textContent; break; }
+	    p = p.previousElementSibling;
+	  }
+	  fetch(`${RELAY_BASE}/rate`, {
+	    method: "POST", headers: { "Content-Type": "application/json" },
+	    body: JSON.stringify({ kind: "chat", rating: value, content: div.dataset.raw || "", context: ctx, session_id: currentSession })
+	  }).catch(() => {});
+	  up.classList.toggle("rated", value === 1);
+	  down.classList.toggle("rated", value === -1);
+	}
+
 	function addMessage(role, text, autoScroll = true) {
 	  const messagesEl = document.getElementById("messages");
 
 	  const msgDiv = document.createElement("div");
 	  msgDiv.className = `msg ${role}`;
-	  if (role === "assistant") { msgDiv.innerHTML = renderMarkdown(text); } else { msgDiv.textContent = text; }
+	  if (role === "assistant") {
+	    msgDiv.innerHTML = renderMarkdown(text);
+	    msgDiv.dataset.raw = text;
+	    addRateBar(msgDiv);
+	  } else {
+	    msgDiv.textContent = text;
+	  }
 	  messagesEl.appendChild(msgDiv);
 
 	  // Auto-scroll to bottom if enabled