feat: add configurable temperature setting

[girmt]

Summary

Adds a defaultTemperature config field to control the model temperature for vision delegation calls. Some providers (e.g. Kimi Code) require a specific temperature value (1) and reject the hardcoded default of 0.

Changes

• lib/config.ts: Added defaultTemperature field (0–2, default 0 for backward compatibility) to VisionConfig, DEFAULT_CONFIG, mergeConfig, and applySettingChange
• lib/delegate.ts: callVisionModel accepts an optional temperature parameter; both callers pass config.defaultTemperature. Falls back to 0 for backward compatibility
• extensions/vision.ts: Added /vision temperature <0-2> subcommand, settings panel row, and display in /vision show

Usage

/vision temperature 1          # set to 1 (Kimi Code requirement)
/vision temperature            # show current value

Or cycle in the settings panel (/vision → Temperature row).