feat: restore remote run cursors

[roackb2]

What changed

• let ConversationRunConsumerService.select(...) initialize a run from a validated afterSequence cursor
• preserve idempotent selection so the current run cannot be rewound or skipped accidentally
• export the additive selection-options type from @roackb2/heddle-remote
• update the hosted browser example to discard and reconstruct its consumer, modeling refresh-style resume
• document cursor persistence and responsibility boundaries in the remote service README

Why

Remote products can persist an accepted run ID and last handled event sequence across a page refresh, but the consumer previously always restarted at sequence 0. That forced a product such as a browser editor to replay the entire retained stream even when it already had a durable cursor.

The cursor state machine already belongs to Heddle's remote consumer service, so this extends that existing boundary instead of adding a second product-specific resume implementation.

Developer impact

Existing callers are unchanged. A reconstructed client can now resume with:

consumer.select(
  { runId: persistedRunId },
  { afterSequence: persistedSequence },
)

The next accepted event must be exactly persistedSequence + 1. Duplicates remain suppressed, gaps still fail loudly, and selecting the same current run again never changes its cursor.

Validation

• targeted consumer tests: 9 passed
• full Heddle tests: 110 unit files / 640 tests; 32 integration files / 291 tests
• yarn typecheck
• yarn eslint
• yarn remote:build
• npm pack ./packages/heddle-remote --dry-run --cache /private/tmp/heddle-remote-npm-cache