feat: persist last-used model in LocalStorage instead of preference

Drop the summaryModel preference (and the awkward textfield holding a
raw model ID nobody could discover without poking the SDK types). Each
AI view now controls its model dropdown, loads the shared
velum.ai.last-model on mount, and writes it back on submit — so picking
Claude 4.7 Opus in the summarize command becomes the prefilled default
in briefing, action-items, structured-data, and reply next time around.

Also drops 'model' from ReplyDefaults; the shared key supersedes it.

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

src/summarize-email.tsx

@@ -14,7 +14,6 @@ import {
 import { copyRichText, markdownToHtml, maybeCloseRaycast } from "./ai-views";
 import { getSelectedTextSafely } from "./selection";
 import { useEffect, useMemo, useRef, useState } from "react";
-import { getPreferences } from "./preferences";
 import {
   createSession,
   getActiveSessionId,
@@ -23,7 +22,13 @@ import {
   setActiveSession,
   updateSessionMapping,
 } from "./sessions";
-import { CREATIVITY_OPTIONS, MODEL_OPTIONS } from "./ai";
+import {
+  CREATIVITY_OPTIONS,
+  DEFAULT_MODEL,
+  getLastUsedModel,
+  MODEL_OPTIONS,
+  setLastUsedModel,
+} from "./ai";
 import { buildSummaryPrompt, type Creativity } from "./summarize";
 import type { EntityType, VelumSession } from "./types";
 import {
@@ -49,23 +54,25 @@ type FormValues = {
 };
 
 export default function Command() {
-  const preferences = getPreferences();
   const [text, setText] = useState("");
   const [sessions, setSessions] = useState<VelumSession[]>([]);
   const [activeSessionId, setActiveSessionId] = useState<string>();
   const [entityTypes, setEntityTypes] = useState<EntityType[]>([]);
   const [selectedEntityTypes, setSelectedEntityTypes] = useState<string[]>([]);
+  const [model, setModel] = useState<string>(DEFAULT_MODEL);
   const [isLoading, setIsLoading] = useState(true);
   const { push } = useNavigation();
 
   useEffect(() => {
     async function load() {
-      const [loadedSessions, activeId] = await Promise.all([
+      const [loadedSessions, activeId, lastModel] = await Promise.all([
         listSessions(),
         getActiveSessionId(),
+        getLastUsedModel(),
       ]);
       setSessions(loadedSessions);
       setActiveSessionId(activeId);
+      setModel(lastModel);
 
       const selection = await getSelectedTextSafely();
       if (selection && selection.trim()) {
@@ -124,6 +131,8 @@ export default function Command() {
       return;
     }
 
+    void setLastUsedModel(values.model);
+
     const toast = await showToast({
       style: Toast.Style.Animated,
       title: "Pseudonymisiere…",
@@ -238,7 +247,8 @@ export default function Command() {
       <Form.Dropdown
         id="model"
         title="KI-Modell"
-        defaultValue={preferences.summaryModel}
+        value={model}
+        onChange={setModel}
       >
         {MODEL_OPTIONS.map((option) => (
           <Form.Dropdown.Item