[TW-6425] fix(@ownmail/app): restore mailbox rendering and draft isolation

[nylas-it-ops]

Summary

• restore authenticated mailbox SSR by placing the React Query provider inside TanStack Router context
• remount the composer by requested draft identity so draft-owned recipients, subject, body, refs, attachments, and autosave state cannot leak between backdrop drafts
• await a fresh draft when mail-version synchronization has invalidated an inactive cached detail
• add an authenticated built-artifact SSR smoke test to CI
• add real router-boundary, same-route draft-switch, and invalidated-cache regression tests
• add an @ownmail/app patch changeset

Root cause

PR #265 moved OwnmailQueryProvider from the root route into TanStack Router's outer Wrap. The provider renders ServerStateSync, which calls useRouterState. Outer Wrap is above RouterContextProvider, so SSR received a null router and failed while reading router.stores.

The change passed because the provider unit tests mocked useRouterState, the router test did not render the provider boundary, and the release smoke test covered packaging rather than a built authenticated SSR request.

The compose backdrop had a separate same-route identity issue: selecting another draft reused the existing Compose instance, leaving draft-owned state and refs initialized from the previous loader result.

Previously opened drafts had a cache freshness issue as well: mail-version sync invalidated inactive draft details, but ensureQueryData returned the cached value without awaiting a refetch. Because compose did not subscribe to that query afterward, stale content could initialize the editor and overwrite a newer server version.

Impact

Authenticated mailbox pages render again instead of returning HTTP 500. Switching between backdrop drafts cannot mix draft identity or metadata, and reopening an externally changed draft initializes from the current server version.

Validation

• pnpm --filter @ownmail/app test — 1,897 tests passed, 100% coverage
• pnpm --filter @ownmail/app typecheck
• pnpm --filter @ownmail/app build:node
• pnpm --filter @ownmail/app smoke:ssr
• pnpm lint — 0 warnings
• pnpm commit:check -- .git/COMMIT_EDITMSG

Jira: TW-6425

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