v.0.1.7 pricing data corrections and internal consistency fixes

v0.1.7

• Fixed incorrect fallback prices for GPT-5.5, GPT-5.4 family, Gemini 3.x, and DeepSeek V4 (verified 2026-06-06)
• Added missing models to fallback: gpt-5.4, gpt-4.1-nano, claude-opus-4-6
• Fixed redundant count_tokens call in /v1/compress route
• Compression failure warnings now route through i18n instead of returning raw strings
• Centralized FEATURED_MODELS into core/featured_models.py, removing duplicate definitions in savings_calculator.py and compress_cmd.py