Support class-based Resource and ResourceTemplate definitions

## Motivation and Context

Resolve the design difference raised in issue #98: Tools and Prompts support class-based definitions
while Resources and Resource Templates were plain data objects requiring a `resources_read_handler` block
with manual URI routing.

`MCP::Resource` and `MCP::ResourceTemplate` now support the same class-level DSL as `MCP::Tool`
and `MCP::Prompt` (`uri`, `resource_name`, `title`, `description`, `icons`, `mime_type`, `annotations`,
`size`, `meta`, and `uri_template` / `resource_template_name` for templates), plus `define` factory methods
and `MCP::Server#define_resource` / `#define_resource_template`.

The default `resources/read` handler now routes requests automatically: an exact URI match calls
the class-based resource's `contents` method, and class-based resource templates match
simple RFC 6570 level 1 `{var}` expressions, passing extracted variables as keyword arguments.
`contents` can opt in to a `server_context:` keyword argument. When class-based entries are registered
and no match is found, the server responds with -32602 carrying the URI in error data per SEP-2164.

## How Has This Been Tested?

- Added regression tests covering the class-level DSL, URI template matching, auto-routing,
  `server_context:` opt-in, error responses, and backward compatibility of the no-op default.
- Verified end-to-end with a smoke script exercising exact-match reads, template-match reads,
  unknown URIs, and legacy instance-only setups.

## Breaking Changes

No. Instance-based registration, `resources_read_handler` precedence, and the no-op `[]` response for
setups without class-based entries are unchanged. Reassigning `Server#resources` now rebuilds
the internal URI index.

Closes #98

lib/mcp/resource.rb

@@ -5,6 +5,141 @@ require_relative "resource/embedded"
 
 module MCP
   class Resource
+    class << self
+      NOT_SET = Object.new
+
+      attr_reader :uri_value
+      attr_reader :title_value
+      attr_reader :description_value
+      attr_reader :icons_value
+      attr_reader :mime_type_value
+      attr_reader :annotations_value
+      attr_reader :size_value
+      attr_reader :meta_value
+
+      def contents(server_context: nil)
+        raise NotImplementedError, "Subclasses must implement contents"
+      end
+
+      def to_h
+        {
+          uri: uri_value,
+          name: name_value,
+          title: title_value,
+          description: description_value,
+          icons: icons_value&.then { |icons| icons.empty? ? nil : icons.map(&:to_h) },
+          mimeType: mime_type_value,
+          annotations: annotations_value&.to_h,
+          size: size_value,
+          _meta: meta_value,
+        }.compact
+      end
+
+      def inherited(subclass)
+        super
+        subclass.instance_variable_set(:@uri_value, nil)
+        subclass.instance_variable_set(:@name_value, nil)
+        subclass.instance_variable_set(:@title_value, nil)
+        subclass.instance_variable_set(:@description_value, nil)
+        subclass.instance_variable_set(:@icons_value, nil)
+        subclass.instance_variable_set(:@mime_type_value, nil)
+        subclass.instance_variable_set(:@annotations_value, nil)
+        subclass.instance_variable_set(:@size_value, nil)
+        subclass.instance_variable_set(:@meta_value, nil)
+      end
+
+      def uri(value = NOT_SET)
+        if value == NOT_SET
+          @uri_value
+        else
+          @uri_value = value
+        end
+      end
+
+      def resource_name(value = NOT_SET)
+        if value == NOT_SET
+          name_value
+        else
+          @name_value = value
+        end
+      end
+
+      def name_value
+        @name_value || (name.nil? ? nil : StringUtils.handle_from_class_name(name))
+      end
+
+      def title(value = NOT_SET)
+        if value == NOT_SET
+          @title_value
+        else
+          @title_value = value
+        end
+      end
+
+      def description(value = NOT_SET)
+        if value == NOT_SET
+          @description_value
+        else
+          @description_value = value
+        end
+      end
+
+      def icons(value = NOT_SET)
+        if value == NOT_SET
+          @icons_value
+        else
+          @icons_value = value
+        end
+      end
+
+      def mime_type(value = NOT_SET)
+        if value == NOT_SET
+          @mime_type_value
+        else
+          @mime_type_value = value
+        end
+      end
+
+      def annotations(value = NOT_SET)
+        if value == NOT_SET
+          @annotations_value
+        else
+          @annotations_value = value.is_a?(Annotations) ? value : Annotations.new(**value)
+        end
+      end
+
+      def size(value = NOT_SET)
+        if value == NOT_SET
+          @size_value
+        else
+          @size_value = value
+        end
+      end
+
+      def meta(value = NOT_SET)
+        if value == NOT_SET
+          @meta_value
+        else
+          @meta_value = value
+        end
+      end
+
+      def define(uri: nil, name: nil, title: nil, description: nil, icons: [], mime_type: nil, annotations: nil, size: nil, meta: nil, &block)
+        Class.new(self) do
+          uri uri
+          resource_name name
+          title title
+          description description
+          icons icons
+          mime_type mime_type
+          self.annotations(annotations) if annotations
+          size size
+          meta meta
+          define_singleton_method(:contents, &block) if block
+        end
+      end
+    end
+
     attr_reader :uri, :name, :title, :description, :icons, :mime_type, :annotations, :size, :meta
 
     def initialize(uri:, name:, title: nil, description: nil, icons: [], mime_type: nil, annotations: nil, size: nil, meta: nil)