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/ThunkToast.svelte

@@ -1,6 +1,5 @@
 <script lang="ts">
   import type {AbstractThunk} from "@welshman/app"
-  import {thunkHasStatus, thunkIsComplete} from "@welshman/app"
   import {PublishStatus} from "@welshman/net"
   import ThunkPending from "@app/components/ThunkPending.svelte"
   import type {Toast} from "@app/toast"
@@ -16,8 +15,8 @@
   const id = toast.id
   const thunk = props.thunk
   const {Aborted, Timeout, Failure} = PublishStatus
-  const isFailure = $derived(thunkHasStatus([Aborted, Timeout, Failure], $thunk))
-  const isComplete = $derived(thunkIsComplete($thunk))
+  const isFailure = $derived($thunk.hasStatus([Aborted, Timeout, Failure]))
+  const isComplete = $derived($thunk.isComplete())
 
   $effect(() => {
     if (isFailure) {