refactor(executor): dedupe thinking metadata helpers across Gemini executors

Extract applyThinkingMetadata and applyThinkingMetadataCLI helpers to
payload_helpers.go and use them across all four Gemini-based executors:
- gemini_executor.go (Execute, ExecuteStream, CountTokens)
- gemini_cli_executor.go (Execute, ExecuteStream, CountTokens)
- aistudio_executor.go (translateRequest)
- antigravity_executor.go (Execute, ExecuteStream)

This eliminates code duplication introduced in the -reasoning suffix PR
and centralizes the thinking config application logic.

Net reduction: 28 lines of code.

internal/runtime/executor/payload_helpers.go

@@ -4,10 +4,42 @@ import (
 	"strings"
 
 	"github.com/router-for-me/CLIProxyAPI/v6/internal/config"
+	"github.com/router-for-me/CLIProxyAPI/v6/internal/util"
 	"github.com/tidwall/gjson"
 	"github.com/tidwall/sjson"
 )
 
+// applyThinkingMetadata applies thinking config from model suffix metadata (e.g., -reasoning, -thinking-N)
+// for standard Gemini format payloads. It normalizes the budget when the model supports thinking.
+func applyThinkingMetadata(payload []byte, metadata map[string]any, model string) []byte {
+	budgetOverride, includeOverride, ok := util.GeminiThinkingFromMetadata(metadata)
+	if !ok {
+		return payload
+	}
+	if !util.ModelSupportsThinking(model) {
+		return payload
+	}
+	if budgetOverride != nil {
+		norm := util.NormalizeThinkingBudget(model, *budgetOverride)
+		budgetOverride = &norm
+	}
+	return util.ApplyGeminiThinkingConfig(payload, budgetOverride, includeOverride)
+}
+
+// applyThinkingMetadataCLI applies thinking config from model suffix metadata (e.g., -reasoning, -thinking-N)
+// for Gemini CLI format payloads (nested under "request"). It normalizes the budget when the model supports thinking.
+func applyThinkingMetadataCLI(payload []byte, metadata map[string]any, model string) []byte {
+	budgetOverride, includeOverride, ok := util.GeminiThinkingFromMetadata(metadata)
+	if !ok {
+		return payload
+	}
+	if budgetOverride != nil && util.ModelSupportsThinking(model) {
+		norm := util.NormalizeThinkingBudget(model, *budgetOverride)
+		budgetOverride = &norm
+	}
+	return util.ApplyGeminiCLIThinkingConfig(payload, budgetOverride, includeOverride)
+}
+
 // applyPayloadConfig applies payload default and override rules from configuration
 // to the given JSON payload for the specified model.
 // Defaults only fill missing fields, while overrides always overwrite existing values.