provider(upstage): add Solar Pro 4 (#4124)

Add solar-pro4 (alias of solar-pro4-260806, released 2026-08-06):
512K context, 128K max output, reasoning on by default with
none/minimal/low/medium/high/xhigh/max effort levels, tool calling
and structured outputs. Pricing $0.30/$1.20 per 1M tokens
($0.06 cached input). Specs from console.upstage.ai model catalog.

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

providers/upstage/models/solar-pro4.toml

@@ -0,0 +1,26 @@
+name = "Solar Pro 4"
+description = "Upstage's flagship model, specialized for agentic use"
+family = "solar-pro"
+release_date = "2026-08-06"
+last_updated = "2026-08-06"
+attachment = false
+reasoning = true
+reasoning_options = [{ type = "effort", values = ["none", "minimal", "low", "medium", "high", "xhigh", "max"] }]
+temperature = true
+knowledge = "2026-02"
+tool_call = true
+structured_output = true
+open_weights = false
+
+[cost]
+input = 0.30
+output = 1.20
+cache_read = 0.06
+
+[limit]
+context = 524_288
+output = 131_072
+
+[modalities]
+input = ["text"]
+output = ["text"]