fix(catalog): write NUL key separators as escape sequences instead of raw bytes (#12403)

Four files embedded the U+0000 separator of a memo/group key as a raw NUL byte rather than the \\0 escape the codebase uses for the same idiom elsewhere. The runtime value is identical, but the raw byte trips the binary heuristics of git, GitHub and ripgrep: git diff --numstat reported `-  -`, the introducing PRs rendered three of the files as "Binary file not shown", and rg silently skipped them in recursive mode. Rewritten as escapes, with a guard test keeping raw NUL bytes out of src/, open-sse/ and tests/.

Validated in a combined worktree with all 25 PRs of this batch boarded together: typecheck:core clean, 443/443 node-runner tests plus 14/14 vitest across every test file the batch touches, and check-changelog-integrity, check:cycles (418 files), check:provider-consistency (272 REGISTRY entries, 355 canonical providers), check:docs-counts, check:docs-sync (42 locales) and check-file-size all green.

Thanks @pacocartones.