gollm: ollama provider breaks against ollama >= 0.20 API

gollm's go.mod pins github.com/ollama/ollama v0.6.5; ollama v0.20.x changed the api package such that gollm/ollama.go no longer compiles: ToolCallFunctionArguments changed from map[string]any to a struct (ollama.go:284), ToolFunctionParameters struct shape changed so the inline literal no longer assigns (ollama.go:307), and Properties became *ToolPropertiesMap instead of an indexable map (ollama.go:328). Downstream consumers can't bump ollama (directly or transitively) until gollm migrates. Ask: update ollama.go to the >= 0.20 API and bump the pin. Mention we hit this via dependabot in a consumer repo.