Migrate to new @welshman/domain + instance-based @welshman/app API

Adopts the rewritten welshman API: the removed @welshman/util helpers
(Profile/List/Room/Handler/Encryptable) are now Reader/Builder classes in
@welshman/domain, and @welshman/app dropped its global singletons for an App
instance + app.use(Plugin) registry.

- src/app/welshman.ts is now the app bootstrap + session-state module (one shared
  App instance, multi-account sessions/login, app-wide reactive views) rather than
  a compat shim re-exporting the old globals.
- Rewrote ~100 callers to use app.use(Plugin) directly (thunks, profiles, relays,
  rooms, zaps, tags, wot, feeds, sync); thunk helpers are now thunk methods.
- Added @welshman/domain dependency.
- Resolved residual gaps (storage hydration via plugin.onItem/wrapManager/Plaintext,
  relay-list mutators, search-relay list, outbox #d filter).

Best-effort: no toolchain/linking available, so this is not build- or
type-checked. Remaining judgment calls are flagged with TODO(welshman-migration).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BsMjvv7krpZeHK1Njeneru

src/app/components/VoiceRoomItem.svelte

@@ -1,7 +1,8 @@
 <script lang="ts">
   import cx from "classnames"
   import {goto} from "$app/navigation"
-  import {loadProfile, displayProfileByPubkey} from "@welshman/app"
+  import {Profiles} from "@welshman/app"
+  import {app} from "@app/welshman"
   import SecondaryNavItem from "@lib/components/SecondaryNavItem.svelte"
   import ProfileCircle from "@app/components/ProfileCircle.svelte"
   import ProfileCircles from "@app/components/ProfileCircles.svelte"
@@ -65,7 +66,7 @@
 
   $effect(() => {
     for (const p of $participants) {
-      if (p.pubkey) loadProfile(p.pubkey)
+      if (p.pubkey) app.use(Profiles).load(p.pubkey)
     }
   })
 </script>
@@ -98,7 +99,7 @@
               <ProfileCircle pubkey={p.pubkey} size={5} class="h-5 w-5" />
             </div>
             <span class="ellipsize min-w-0 flex-1 text-xs opacity-70">
-              {p.pubkey ? displayProfileByPubkey(p.pubkey) : "Unknown"}
+              {p.pubkey ? app.use(Profiles).display(p.pubkey).get() : "Unknown"}
             </span>
             <VoiceParticipantMediaBadges
               muted={media.muted}