[BOT ISSUE] fix: update stale pricing for openai/gpt-oss-120b

Stale pricing

The model openai/gpt-oss-120b has outdated pricing in the catalog (packages/proxy/schema/model_list.json).

Current vs correct pricing

Field	Catalog value	Correct value
Input cost (per 1M tokens)	$0.10	$0.15
Output cost (per 1M tokens)	$0.50	$0.60

Verification checklist

• Cross-source confirmation: Updated pricing confirmed on both Groq pricing page ($0.15/$0.60) and Together AI pricing page ($0.15/$0.60).
• Recent commits check: Not corrected in any of the last 30 commits touching model_list.json.
• ID format validation: Model already exists in catalog (lines 1532-1547), ID format is correct.

Notes

• Previous issue [BOT ISSUE] Groq openai/gpt-oss-120b pricing differs from official Groq docs #479 reported this same discrepancy but was closed without updating the catalog prices.

Prepared catalog updates for openai/gpt-oss-120b. Updated models: openai/gpt-oss-120b.

Verification sources: https://www.together.ai/pricing, https://groq.com/pricing/
Verified metadata applied:

• openai/gpt-oss-120b: format=openai, flavor=chat, displayName=OpenAI GPT-OSS (120B), max_input_tokens=131072, max_output_tokens=32766, pricing(input/output per 1M)=0.15/0.6, input_cache_read_cost_per_mil_tokens=0.075, providers=groq|together|baseten, reasoning=true

Opened #580 to apply the catalog update.