refactor: replace mcp-go with the official MCP Go SDK (#223)

## Summary

Replace `github.com/mark3labs/mcp-go` with the official
`github.com/modelcontextprotocol/go-sdk v1.7.0`.

All 54 existing tools, scopes, CLI, `stdio` and HTTP (`/mcp`) modes, and
per-request authentication remain supported. This PR is limited to the SDK
equivalence migration; the stateless 2026 HTTP transport is deferred to a
follow-up PR.

## Verification

- Tool definitions were compared with `main` and matched for all 54 tools.
- `make lint`, `make fmt`, `go test -count=1 -race ./...`, `make build`, and
  `make tidy` pass.

---------

Co-authored-by: bircni <bircni@icloud.com>
Co-authored-by: silverwind <me@silverwind.io>
Reviewed-on: https://gitea.com/gitea/gitea-mcp/pulls/223
Reviewed-by: silverwind <2021+silverwind@noreply.gitea.com>
Reviewed-by: bircni <bircni@icloud.com>
Co-authored-by: Bo-Yi Wu <appleboy.tw@gmail.com>

pkg/tool/definition.go

@@ -0,0 +1,106 @@
+package tool
+
+import "github.com/modelcontextprotocol/go-sdk/mcp"
+
+// Property describes one property in a tool's input schema.
+type Property struct {
+	name     string
+	schema   map[string]any
+	required bool
+}
+
+// PropertyOption configures one property in a tool's input schema.
+type PropertyOption func(*Property)
+
+// NewDefinition builds a tool definition without enabling SDK-side validation.
+func NewDefinition(name, description string, annotations *mcp.ToolAnnotations, properties ...Property) *mcp.Tool {
+	inputProperties := make(map[string]any, len(properties))
+	required := make([]string, 0, len(properties))
+	for _, property := range properties {
+		inputProperties[property.name] = property.schema
+		if property.required {
+			required = append(required, property.name)
+		}
+	}
+
+	inputSchema := map[string]any{
+		"type":       "object",
+		"properties": inputProperties,
+	}
+	if len(required) > 0 {
+		inputSchema["required"] = required
+	}
+
+	return &mcp.Tool{
+		Name:        name,
+		Description: description,
+		Annotations: annotations,
+		InputSchema: inputSchema,
+	}
+}
+
+func String(name string, options ...PropertyOption) Property {
+	return newProperty(name, map[string]any{"type": "string"}, options...)
+}
+
+func Number(name string, options ...PropertyOption) Property {
+	return newProperty(name, map[string]any{"type": "number"}, options...)
+}
+
+func Boolean(name string, options ...PropertyOption) Property {
+	return newProperty(name, map[string]any{"type": "boolean"}, options...)
+}
+
+func Array(name string, options ...PropertyOption) Property {
+	return newProperty(name, map[string]any{"type": "array"}, options...)
+}
+
+func Object(name string, options ...PropertyOption) Property {
+	return newProperty(name, map[string]any{"type": "object", "properties": map[string]any{}}, options...)
+}
+
+func newProperty(name string, schema map[string]any, options ...PropertyOption) Property {
+	property := Property{name: name, schema: schema}
+	for _, option := range options {
+		option(&property)
+	}
+	return property
+}
+
+// Required marks the property as required on the parent schema. It is not a
+// property-level keyword, so it never touches the emitted property schema.
+func Required() PropertyOption {
+	return func(property *Property) {
+		property.required = true
+	}
+}
+
+func Description(description string) PropertyOption {
+	return func(property *Property) {
+		property.schema["description"] = description
+	}
+}
+
+func Enum(values ...string) PropertyOption {
+	return func(property *Property) {
+		property.schema["enum"] = values
+	}
+}
+
+func Default(value any) PropertyOption {
+	return func(property *Property) {
+		property.schema["default"] = value
+	}
+}
+
+func Minimum(value float64) PropertyOption {
+	return func(property *Property) {
+		property.schema["minimum"] = value
+	}
+}
+
+func Items(schema any) PropertyOption {
+	return func(property *Property) {
+		property.schema["items"] = schema
+	}
+}