feat: switch LLM to OpenWebUI with live model selection

- Point the agent at OpenWebUI's OpenAI-compatible API (LLM_BASE_URL,
  LLM_API_KEY, LLM_MODEL) with GEMMA_* env fallbacks
- Add list_available_models() fetching {base_url}/models, filtering
  non-chat ids (embedding/reranker)
- Rename GemmaLLM -> HopeLLM with update_options(model=...) for runtime
  model switching (mutates _opts.model) and instance-based compaction
- Data channel: agent publishes {type: models} after connect and on
  get_models; set_model switches live and acks model_changed
- Web UI: Brain section in the settings sheet with a model picker that
  persists the choice in localStorage
- Update tests, CI workflow env, and docs for the new endpoint

web/app.js

@@ -27,6 +27,7 @@ const VOICES = [
 const HISTORY_KEY = "voice_history";
 const HISTORY_MAX = 50;
 const MODE_KEY = "hope_conversation_mode";
+const MODEL_KEY = "preferred_model";
 
 // ── State ───────────────────────────────────────────────────────────────────
 let room = null;
@@ -40,6 +41,10 @@ let wakeLock = null;
 let conversationMode = localStorage.getItem(MODE_KEY) === "text" ? "text" : "voice";
 let connectionPromise = null;
 
+// ── Model (brain) state — populated from the agent's data channel ──────────
+let availableModels = [];          // ids published by the agent
+let selectedModel = localStorage.getItem(MODEL_KEY) || null;
+
 function escapeHtml(s) {
     const d = document.createElement("div");
     d.textContent = s || "";
@@ -63,6 +68,8 @@ const settingsSheet = document.getElementById("settingsSheet");
 const sheetBackdrop = document.getElementById("sheetBackdrop");
 const closeSheetBtn = document.getElementById("closeSheetBtn");
 const voiceListEl = document.getElementById("voiceList");
+const modelListEl = document.getElementById("modelList");
+const modelNoteEl = document.getElementById("modelNote");
 const clearBtn = document.getElementById("clearBtn");
 const tasksBtn = document.getElementById("tasksBtn");
 const tasksPanel = document.getElementById("tasksPanel");
@@ -547,8 +554,20 @@ function handleDataPacket(payload, participant, topic) {
             }
         } else if (msg.type === "task_event") {
             handleTaskEvent(msg);
+        } else if (msg.type === "models") {
+            availableModels = Array.isArray(msg.models) ? msg.models : [];
+            // Don't clobber a saved preference — the agent acks the applied
+            // model separately via model_changed.
+            if (!selectedModel && msg.selected) selectedModel = msg.selected;
+            renderModelList();
+        } else if (msg.type === "model_changed") {
+            if (msg.model) {
+                selectedModel = msg.model;
+                localStorage.setItem(MODEL_KEY, selectedModel);
+                renderModelList();
+            }
         }
-        // set_voice messages flow the other way; nothing to do client-side.
+        // set_voice/set_model messages flow the other way; nothing else to do client-side.
     } catch (e) {
         console.warn("bad data packet", e);
     }
@@ -598,8 +617,61 @@ function selectVoice(voiceId) {
     }
 }
 
+// ── Model (brain) settings ──────────────────────────────────────────────────
+function currentModelId() {
+    if (availableModels.length === 0) return selectedModel;
+    if (selectedModel && availableModels.includes(selectedModel)) return selectedModel;
+    return availableModels[0];
+}
+
+function renderModelList() {
+    modelListEl.innerHTML = "";
+    if (!availableModels.length) {
+        modelNoteEl.hidden = false;
+        modelNoteEl.textContent = room
+            ? "Loading available models…"
+            : "Start a conversation to load the model list.";
+        return;
+    }
+    modelNoteEl.hidden = true;
+    const active = currentModelId();
+    for (const id of availableModels) {
+        const card = document.createElement("div");
+        card.className = "voice-card" + (id === active ? " active" : "");
+        card.dataset.model = id;
+        card.setAttribute("role", "radio");
+        card.setAttribute("aria-checked", String(id === active));
+        card.tabIndex = 0;
+
+        const name = document.createElement("span");
+        name.className = "voice-name";
+        name.textContent = id;
+
+        card.appendChild(name);
+        card.addEventListener("click", () => selectModel(id));
+        card.addEventListener("keydown", (event) => {
+            if (event.key === "Enter" || event.key === " ") {
+                event.preventDefault();
+                selectModel(id);
+            }
+        });
+        modelListEl.appendChild(card);
+    }
+}
+
+function selectModel(modelId) {
+    selectedModel = modelId;
+    localStorage.setItem(MODEL_KEY, modelId);
+    renderModelList();
+    if (room && agentParticipant) {
+        sendModelMessage(modelId);
+        addMessage("system", `Brain changed to ${modelId}`);
+    }
+}
+
 function openSheet() {
     renderVoiceList();
+    renderModelList();
     sheetBackdrop.hidden = false;
     settingsSheet.classList.add("open");
     settingsBtn.setAttribute("aria-expanded", "true");
@@ -665,8 +737,9 @@ function markAgentFound(rm, participant) {
     statusEl.textContent = conversationMode === "text"
         ? "Hope joined · Text chat ready"
         : "Hope joined · Preparing microphone…";
-    // Synchronize voice and interaction mode when the agent joins.
+    // Synchronize voice, brain and interaction mode when the agent joins.
     sendVoiceMessage(currentVoiceId(), rm);
+    if (selectedModel) sendModelMessage(selectedModel, rm);
     sendModeMessage(conversationMode, rm);
 }
 
@@ -980,3 +1053,14 @@ function sendModeMessage(mode, targetRoom) {
         reliable: true,
     });
 }
+
+// ── Helper: send model selection to the agent via data channel ─────────────
+function sendModelMessage(model, targetRoom) {
+    const r = targetRoom || room;
+    if (!r || !r.localParticipant || !model) return;
+    const payload = new TextEncoder().encode(JSON.stringify({ type: "set_model", model }));
+    r.localParticipant.publishData(payload, {
+        topic: "voice-control",
+        reliable: true,
+    });
+}