refactor(adapters): extract escapeYamlValue into shared util and fix \r escape gap

[coderabbitai]

Summary

The escapeYamlValue helper is currently duplicated verbatim across three adapter files:

• src/core/command-generation/adapters/pi.ts
• src/core/command-generation/adapters/claude.ts
• src/core/command-generation/adapters/qwen.ts

There is also a known detect/escape asymmetry: \r (carriage return) is correctly detected as requiring YAML quoting (via the regex), but is not escaped in the double-quoted string replace chain. This gap exists consistently across all three siblings.

Proposed Work

1. Extract escapeYamlValue into a shared utility (e.g., src/core/command-generation/utils/yaml.ts or similar).
2. Add \r → \\r escaping in the shared implementation so double-quoted YAML strings fully conform to YAML 1.2.
3. Update pi.ts, claude.ts, and qwen.ts to import and use the shared helper instead of their local copies.
4. Add or update unit tests for the shared utility to cover the \r case.

Context

• Discussed in PR fix(qwen): generate Markdown commands instead of deprecated TOML format #1191 (comment: fix(qwen): generate Markdown commands instead of deprecated TOML format #1191 (comment))
• The \r fix was intentionally deferred from PR fix(qwen): generate Markdown commands instead of deprecated TOML format #1191 to avoid diverging the qwen adapter copy from its siblings before a proper shared-util refactor.

Requested by: @mc856