#2702 serve: protect remaining input call literals

说明

# Issue: Literal call markers in input can become protocol tokens

Follow up #2026 on v0.1.44.1 (296b59d2). Nested JSON keys and structured assistant
arguments are not all protected by the input-literal marking path.
Expected: data remains data; actual template call framing remains protocol.

# PR: Protect remaining input call literals

Extend the existing marking path to nested keys and structured arguments.
Preserve upstream's call/response tag mapping, outer tool-result wrappers,
raw assistant content semantics and caller-owned objects.

Validation: `serve.test_quote_call_literals`; ordinary tokenizer IDs for literals,
real framing, nested data and unchanged-input controls. With upstream
`serve.test_frontend`: 33 tests pass. The added regressions fail on unmodified
296b59d2 (six assertion failures, including subtests).