fix(vault): surface operation failures

[vutuanlinh2k2]

Summary

• surface list, save, create, and delete failures through retryable Vault UI states
• preserve drafts, dialogs, selections, and the last loaded tree across rejected operations
• handle post-mutation refresh failures without repeating successful creates or deletes
• expose an optional structured onOperationError callback for host telemetry

Testing

• pnpm typecheck
• pnpm vitest run tests/vault/vault-pane.test.ts — 33 tests passed
• pnpm exec vitest run --exclude src/sandbox/index.test.ts
• NODE_OPTIONS=--max-old-space-size=8192 pnpm build

The unfiltered suite still has three pre-existing deferred-file/base64 failures in src/sandbox/index.test.ts; the changed Vault suite and all other test files pass.

Closes #181