ux: rename model fields + enforce serial curator execution

Three coordinated changes per operator request 2026-05-24:

1. Settings UI rename matching the language we actually use:
   - Chat Model -> Chat & Voice Model
   - Worker Model -> Curator Model
   Setting KEYS (default_model / background_model) unchanged on
   purpose; renaming them requires a migration touching 50+ call
   sites for purely UX-facing benefit.

2. Settings UI help text rewritten:
   - Chat & Voice: documents that it handles chat AND small
     conversational automations (titles, tags). Recommends
     OLLAMA_NUM_PARALLEL=2+ on the Ollama server so background
     automations get their own KV-cache slot and don't evict
     the chat model's working state.
   - Curator: notes the app enforces SERIAL execution regardless
     of NUM_PARALLEL — only one curator pass runs at a time. This
     matters most for 70b CPU models where a second instance
     would waste system RAM.

3. Enforce serial curator execution globally:
   - New module-level _CURATOR_RUN_LOCK in services/curator.py.
   - run_curator_for_conversation now wraps its body in 'async
     with _CURATOR_RUN_LOCK' — every entry point (scheduler sweep,
     manual route trigger, future hooks) is serialized through it.
   - is_curator_running() helper exposes the lock state.
   - routes/journal.py manual trigger checks is_curator_running()
     first and returns 409 {busy: true} immediately rather than
     blocking the HTTP request for minutes waiting for a 70b CPU
     pass to finish. The user can retry once the curator clears.

   Why a 409 instead of queue: a curator pass on a 70b CPU model
   can take 5+ minutes. Tying up an HTTP worker that long is bad;
   making the user wait without feedback is worse. 409 surfaces
   the busy state immediately and the user retries when they want.

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

frontend/src/views/SettingsView.vue

@@ -1535,28 +1535,32 @@ function formatUserDate(iso: string): string {
             <p class="field-hint">The name used in chat messages and LLM context.</p>
           </div>
           <div class="field">
-            <label for="default-model">Chat Model</label>
+            <label for="default-model">Chat &amp; Voice Model</label>
             <select id="default-model" v-model="defaultModel" class="input">
               <option value="">Default ({{ defaultChatModel || "qwen3:latest" }})</option>
               <option v-for="m in installedModels" :key="m" :value="m">{{ m }}</option>
             </select>
             <p class="field-hint">
-              Used for journal chat (no tools — just conversation) and lightweight one-shot tasks like note-title generation and tag suggestions.
-              Pick a small fast model (e.g. <code>qwen3:8b</code>, <code>llama3.2:3b</code>) — speed matters more than depth here.
+              Powers the journal conversation (typed or voice-driven) AND small conversational automations: note-title generation, tag suggestions.
+              Pick a small fast model (e.g. <code>qwen3:8b</code>, <code>llama3.2:3b</code>) — speed and responsiveness matter more than depth.
               Ideally runs on GPU.
+              <br><br>
+              <strong>Tip for snappy chat:</strong> set <code>OLLAMA_NUM_PARALLEL=2</code> (or higher) on your Ollama server so background automations (tags, titles) get their own KV-cache slot and don't evict the chat model's working state. With <code>NUM_PARALLEL=1</code>, every background call pauses the chat and re-warms the prompt on the next user turn.
             </p>
           </div>
           <div class="field">
-            <label for="background-model">Worker Model</label>
+            <label for="background-model">Curator Model</label>
             <select id="background-model" v-model="backgroundModel" class="input">
               <option value="">Default (qwen3:latest)</option>
               <option v-for="m in installedModels" :key="m" :value="m">{{ m }}</option>
             </select>
             <p class="field-hint">
-              Used for heavy async work: the journal curator (capture / propose updates), daily prep generation, end-of-day closeout, task body consolidation, project summaries, and profile observation processing.
-              Pick a smart model — latency doesn't matter, quality does. Often runs on CPU with system RAM (e.g. <code>qwen3:32b</code>, <code>qwen3:30b-a3b</code>).
+              Powers the journal curator (capture moments, propose updates) and other heavy async work: daily prep generation, end-of-day closeout, task body consolidation, project summaries, profile observation processing.
+              Pick a smart model — latency doesn't matter, quality does. Often runs on CPU with system RAM (e.g. <code>qwen3:32b</code>, <code>qwen3:30b-a3b</code>, <code>llama3.1:70b</code>).
+              <br><br>
+              <strong>Serialized:</strong> the app enforces one curator pass at a time globally, regardless of <code>OLLAMA_NUM_PARALLEL</code>. Manual triggers fired while the curator is busy return a "try again" response rather than spawning a second instance. This matters most for large CPU models where a second KV-cache slot would waste system RAM.
               <span v-if="backgroundModel && backgroundModel === (defaultModel || defaultChatModel)" class="field-hint-warn">
-                ⚠ Using the same model for both means worker tasks compete for the chat model's resources. Pick different models so they can be loaded simultaneously (<code>OLLAMA_MAX_LOADED_MODELS&nbsp;=&nbsp;2</code>+).
+                ⚠ Using the same model for both means curator passes compete with chat for the same KV cache. Pick different models so both can stay loaded simultaneously (<code>OLLAMA_MAX_LOADED_MODELS&nbsp;=&nbsp;2</code>+).
               </span>
             </p>
           </div>