stripModelProfileSuffix() in providers.ts naively truncated model names at
the first '@', discarding quant variants like @iq3_xxs, @iq4_xs, @q4_k_xl
that LM Studio uses to distinguish quantization levels.
This caused two user-facing bugs (fixes#71474):
1. /model lmstudio/qwen3.6-27b@iq3_xxs → 'model not allowed: lmstudio/qwen3.6-27b'
2. API requests sent truncated model name → LM Studio picked a random quant
Changes:
- Replace the naive indexOf('@') strip in providers.ts with
splitTrailingAuthProfile() which already handles quant suffixes
- Extend the quant-suffix regex (q\d+...) to also match importance-
quantization tags (iq3_xxs, iq4_xs, ...) via i?q\d+ pattern
- Add tests for @iq* quant suffixes and auth-profile-after-iq combos