feat: accept string values for all numeric input parameters (#138)

## Summary

- MCP clients may send numbers as strings. This adds `ToInt64` and `GetOptionalInt` helpers to `pkg/params` and replaces all raw `.(float64)` type assertions across operation handlers to accept both `float64` and string inputs.

## Test plan

- [x] Verify `go test ./...` passes
- [x] Test with an MCP client that sends numeric parameters as strings

*Created by Claude on behalf of @silverwind*

Reviewed-on: https://gitea.com/gitea/gitea-mcp/pulls/138
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-committed-by: silverwind <me@silverwind.io>

pkg/params/params.go

@@ -5,7 +5,24 @@ import (
 	"strconv"
 )
 
-// GetIndex extracts an index parameter from MCP tool arguments.
+// ToInt64 converts a value to int64, accepting both float64 (JSON number) and
+// string representations. Returns false if the value cannot be converted.
+func ToInt64(val any) (int64, bool) {
+	switch v := val.(type) {
+	case float64:
+		return int64(v), true
+	case string:
+		i, err := strconv.ParseInt(v, 10, 64)
+		if err != nil {
+			return 0, false
+		}
+		return i, true
+	default:
+		return 0, false
+	}
+}
+
+// GetIndex extracts a required integer parameter from MCP tool arguments.
 // It accepts both numeric (float64 from JSON) and string representations.
 // This provides better UX for LLM callers that may naturally use strings
 // for identifiers like issue/PR numbers.
@@ -15,19 +32,27 @@ func GetIndex(args map[string]any, key string) (int64, error) {
 		return 0, fmt.Errorf("%s is required", key)
 	}
 
-	// Try float64 (JSON number type)
-	if f, ok := val.(float64); ok {
-		return int64(f), nil
+	if i, ok := ToInt64(val); ok {
+		return i, nil
 	}
 
-	// Try string and parse to integer
 	if s, ok := val.(string); ok {
-		i, err := strconv.ParseInt(s, 10, 64)
-		if err != nil {
-			return 0, fmt.Errorf("%s must be a valid integer (got %q)", key, s)
-		}
-		return i, nil
+		return 0, fmt.Errorf("%s must be a valid integer (got %q)", key, s)
 	}
 
 	return 0, fmt.Errorf("%s must be a number or numeric string", key)
 }
+
+// GetOptionalInt extracts an optional integer parameter from MCP tool arguments.
+// Returns defaultVal if the key is missing or the value cannot be parsed.
+// Accepts both float64 (JSON number) and string representations.
+func GetOptionalInt(args map[string]any, key string, defaultVal int64) int64 {
+	val, exists := args[key]
+	if !exists {
+		return defaultVal
+	}
+	if i, ok := ToInt64(val); ok {
+		return i
+	}
+	return defaultVal
+}