feat: coordinate causal changes with editable input

[developer-1px]

Summary

• expose an additive getJsonEditableDocumentHost(editor) capability while preserving the established JsonEditable and mount contracts
• arbitrate causal ready changes against native input, browser event turns, active publications, IME ownership, damaged composition recovery, and teardown
• assign monotonic pre-commit ownership sequences for native/app/history/ready publications and isolate user callback failures so causal journals cannot miss an owned change
• dogfood the merged json-document causal/rebase packages from SHA-pinned tarballs with checksums, coalesced idle retry, and a delayed-edit demo tracer

Verification

• pnpm run verify:internal — 12 files / 111 tests, TypeScript, layer check, Biome, production build
• pnpm run verify:browser — 45 tests across Chromium, Firefox, and WebKit
• pnpm install --frozen-lockfile
• shasum -a 256 -c vendor/json-document-e8d572d4/SHA256SUMS
• independent host, integration, and adversarial reviews: no remaining blockers

Upstream artifacts are built from merged json-document commit e8d572d4af1d6570dde2783972e40b9f914236c2 (developer-1px/json-document#232).