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/ThreadPost.svelte

@@ -1,8 +1,9 @@
 <script lang="ts">
   import {formatTimestamp} from "@welshman/lib"
   import type {TrustedEvent} from "@welshman/util"
-  import {COMMENT} from "@welshman/util"
-  import {deriveHandleForPubkey, deriveProfileDisplay, displayHandle} from "@welshman/app"
+  import {COMMENT, displayNip05} from "@welshman/util"
+  import {Handles, Profiles} from "@welshman/app"
+  import {app} from "@app/welshman"
   import Reply from "@assets/icons/reply-2.svg?dataurl"
   import LinkRound from "@assets/icons/link-round.svg?dataurl"
   import Icon from "@lib/components/Icon.svelte"
@@ -26,8 +27,8 @@
 
   const {url, event, threadPubkey, onReply}: Props = $props()
 
-  const profileDisplay = deriveProfileDisplay(event.pubkey, [url])
-  const handle = deriveHandleForPubkey(event.pubkey)
+  const profileDisplay = app.use(Profiles).display(event.pubkey, [url]).$
+  const handle = app.use(Handles).forPubkey(event.pubkey).$
   const isOp = event.pubkey === threadPubkey
   const isComment = event.kind === COMMENT
 
@@ -53,7 +54,7 @@
           {$profileDisplay}
         </Button>
         {#if $handle}
-          <span class="ellipsize text-xs opacity-75">{displayHandle($handle)}</span>
+          <span class="ellipsize text-xs opacity-75">{displayNip05($handle?.nip05)}</span>
         {/if}
         {#if isOp}
           <span class="badge badge-primary badge-sm">OP</span>