profile: drop unused title/signature/defaultAgentId fields

These were aspirational placeholders — stored to localStorage but never
read by anything. Removed from the form, types, and persistence layer.
Local profile is now just the avatar URL mirror, which the appbar reads
before the server profile fetch resolves on mount.

Preferences card renamed to "Avatar" since that's all that's left.
Re-add server-backed if/when something actually consumes them.

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

app/lib/profile.ts

@@ -1,23 +1,16 @@
-// Local user preferences — title, signature, default agent, plus a cache
-// mirror of the resolved avatar URL. Persisted in localStorage; reactive
-// across tabs. Identity (name, email) is owned by the arcadia session
-// (~/lib/session.ts); the public profile (bio, phone, location, timezone)
-// is server-backed via /api/v1/profile (~/lib/arcadia/profiles.ts).
+// Local mirror of the resolved avatar URL, so the appbar can render the
+// avatar before the profile fetch resolves on next mount. The real
+// profile (name, email, bio, phone, location, timezone, avatar) is
+// server-backed — see ~/lib/arcadia/profiles.ts.
 
 import { useEffect, useSyncExternalStore } from "react"
 
 export type Profile = {
-  title: string
-  signature: string
   avatarUrl: string
-  defaultAgentId: string
 }
 
 export const DEFAULT_PROFILE: Profile = {
-  title: "",
-  signature: "",
   avatarUrl: "",
-  defaultAgentId: "",
 }
 
 const STORAGE_KEY = "crema.profile"
@@ -30,20 +23,10 @@ function readFromStorage(): Profile {
     if (!raw) return DEFAULT_PROFILE
     const parsed = JSON.parse(raw) as Partial<Profile>
     return {
-      title:
-        typeof parsed.title === "string" ? parsed.title : DEFAULT_PROFILE.title,
-      signature:
-        typeof parsed.signature === "string"
-          ? parsed.signature
-          : DEFAULT_PROFILE.signature,
       avatarUrl:
         typeof parsed.avatarUrl === "string"
           ? parsed.avatarUrl
           : DEFAULT_PROFILE.avatarUrl,
-      defaultAgentId:
-        typeof parsed.defaultAgentId === "string"
-          ? parsed.defaultAgentId
-          : DEFAULT_PROFILE.defaultAgentId,
     }
   } catch {
     return DEFAULT_PROFILE