* fix(toml): escape control characters so generated command files parse
both toml renderers (TomlIntegration._render_toml_string for gemini/tabnine
and CommandRegistrar.render_toml_command for extension/preset commands) wrote
control characters raw into a multiline or basic string. toml forbids literal
control chars (U+0000-U+001F except tab/newline, and U+007F) in every string
form, and a bare CR that is not part of a CRLF pair, so a description or body
containing one produced a .toml file that fails to parse.
route any value with such a character to a fully-escaped basic string that
emits the leftover control chars as \uXXXX. added regression tests that
round-trip through tomllib.
* refactor(toml): centralize control-char escaping in one shared helper
the control-char detection and basic-string escaping added for both toml
renderers were copy-pasted into agents.py and integrations/base.py. move the
two functions into specify_cli/_toml_string.py and have both renderers
delegate to it, so the escaping rules can't drift apart later.
no behavior change; both renderers now reference the same implementation.
