fix: parse ANSI-colored agent --list-models output for /v1/models

When the proxy inherits FORCE_COLOR=1, agent --list-models emits ANSI
codes that broke model line parsing and returned an empty catalog. Strip
ANSI before parsing, force NO_COLOR for list-models, and skip caching
empty results.

Fixes #28

Co-authored-by: Cursor <cursoragent@cursor.com>