docs(resumable): teach flat root imports instead of removed subpaths

[davideast]

Docs and comments now import stores, probes, and the reconnecting client from @inbrowser/resumable instead of the removed /memory, /rtdb, and /testing subpaths.

import {
  createJobEngine,
  createMemoryJobStore,
  createRtdbJobStore,
  serviceAccountTokenProvider,
  probeStoreDurability,
} from '@inbrowser/resumable';

const engine = createJobEngine({
  store: createMemoryJobStore<{ kind: 'chunk'; text: string }>(),
});

const durable = createRtdbJobStore<{ kind: 'chunk'; text: string }>({
  url: process.env.RTDB_URL!,
  auth: serviceAccountTokenProvider({ keyFile: './service-account.json' }),
  rootPath: 'resumable_jobs',
});

Risk

Low. No exports map or runtime code changes. Reviewers should confirm examples no longer teach sealed deep imports that fail under Node/package exports.

The public surface stays one root barrel

Before (broken under exports)	After
@inbrowser/resumable/memory	@inbrowser/resumable
@inbrowser/resumable/rtdb	@inbrowser/resumable
@inbrowser/resumable/testing	@inbrowser/resumable

Relay docs that still showed /rtdb or /memory for createRtdbJobStore / createMemoryJobStore were updated the same way. Module headers and test comments match the root-only map.

Implementation notes and verification

• Touched resumable README/Diataxis docs, source headers, and relay tutorial/README/how-to-wire examples.
• Declined re-opening ./engine or ./store/idb: the APIs already ship from ..
• No packaging smoke change required; import paths in published code were already root-only.