docs(code-runtime-python): split the deadlock into its own bullet and qualify the done_value claim

Addresses the review's two registration-text accuracy findings:
- The cross-thread t.join() deadlock is a process-isolation-backend property (the
  pump runs on the child's main event loop), so it is split out of the wide-binding
  REPLY bullet into its own Known Limitations entry with the correct attribution
  (fix belongs in this backend, not packages/core/session); the zh half-width
  space is removed.
- The settlement note's _done_with_value def-time default-arg sentence is
  qualified: it guards a rebind of _check_done_value/_encode_json_plain, while a
  transitive encoder dep (_dump_scalar/io) rebind can still downgrade, which is
  registered as an accepted residual in the package README.
Pairing re-recorded; corpus-wide verify-translation-pairing passes 1004.

packages/code-runtime/code-runtime-python/README.i18n.yaml

@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write packages/code-runtime/code-runtime-python/README.md
-README.md: 180b0eec9bd5644bfb37086b9eb35cbe93d51672
-README.zh.md: 8a1468f56c62cc1b8544a05c4420270aa26dba31
+README.md: f976b050992863cc8586b5415d9c36cfe193229e
+README.zh.md: 608ac28ecab35f90d9a9d6582e15a24fa4e78c10