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/ChatComposeParent.svelte

@@ -1,6 +1,7 @@
 <script lang="ts">
   import type {TrustedEvent} from "@welshman/util"
-  import {displayProfileByPubkey} from "@welshman/app"
+  import {app} from "@app/welshman"
+  import {Profiles} from "@welshman/app"
   import {slide} from "@lib/transition"
   import CloseCircle from "@assets/icons/close-circle.svg?dataurl"
   import Icon from "@lib/components/Icon.svelte"
@@ -21,7 +22,7 @@
 <div
   class="relative border-l-2 border-solid border-primary bg-base-300 px-2 py-1 pr-8"
   transition:slide>
-  <p class="text-xs text-primary">{verb} @{displayProfileByPubkey(event.pubkey)}</p>
+  <p class="text-xs text-primary">{verb} @{app.use(Profiles).display(event.pubkey).get()}</p>
   {#key event.id}
     <NoteContentMinimal trimParent {event} />
   {/key}