perf(runtime): append ordinary run facts incrementally

[Eclipseic1848]

Summary

• keep a bounded, file-identity-checked cursor for normal FileRunStore.append() calls
• atomically create the first JSONL record, then append one ordinary Fact at a time without rewriting prior history
• retain the existing full-prefix sync plus atomic rename path for critical commits so a failed durability barrier cannot publish an unacknowledged Fact
• invalidate the cursor after external file changes, preserve old-sequence idempotency/conflicts, and keep bounded torn-tail repair
• rebuild the Python bundled Worker and align the durable-run documentation

Verification

• npx vitest run --project coremind-runtime — 800 passed, 2 skipped
• python -X utf8 -m unittest discover -s python/tests -p "test_node_parity.py" — 6 passed
• npm run check — lint, all workspace typechecks, module contracts, docs pairing, and 466-file Markdown audit passed
• independent read-only review found no remaining High issues

Critical commits intentionally retain copy-on-write publication because in-place append cannot preserve the existing guarantee that a failed sync leaves an unacknowledged Fact unpublished without adding a WAL or changing the persistence format.

Closes #161