Add support for forcing GPT-5 Codex model configuration

- Introduced a new `ForceGPT5Codex` configuration option in settings.
- Added relevant API endpoints for managing `ForceGPT5Codex`.
- Enhanced Codex client to handle GPT-5 Codex-specific logic and mapping.
- Updated example configuration file to include the new option.

Add GPT-5 Codex model support and configuration options in documentation

internal/api/handlers/management/config_basic.go

@@ -12,6 +12,14 @@ func (h *Handler) GetConfig(c *gin.Context) {
 func (h *Handler) GetDebug(c *gin.Context) { c.JSON(200, gin.H{"debug": h.cfg.Debug}) }
 func (h *Handler) PutDebug(c *gin.Context) { h.updateBoolField(c, func(v bool) { h.cfg.Debug = v }) }
 
+// ForceGPT5Codex
+func (h *Handler) GetForceGPT5Codex(c *gin.Context) {
+	c.JSON(200, gin.H{"gpt-5-codex": h.cfg.ForceGPT5Codex})
+}
+func (h *Handler) PutForceGPT5Codex(c *gin.Context) {
+	h.updateBoolField(c, func(v bool) { h.cfg.ForceGPT5Codex = v })
+}
+
 // Request log
 func (h *Handler) GetRequestLog(c *gin.Context) { c.JSON(200, gin.H{"request-log": h.cfg.RequestLog}) }
 func (h *Handler) PutRequestLog(c *gin.Context) {