feat(ext-mcp): add MCP (Model Context Protocol) server extension

Streamable HTTP transport (JSON-RPC 2.0 over POST), one-class-per-tool/resource/prompt
API mirroring RequestHandler, boot-time-precompiled schema/list payloads for a zero-alloc
hot path, and optional OAuth2 protection built on flash-ext-oidc (lazy-loaded, RFC 8707
audience binding, RFC 9728 Protected Resource Metadata). Registers the module in the
root and flash-extensions POMs and adds the ext-mcp commit scope to AGENTS.md.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

pom.xml

@@ -97,6 +97,11 @@
                 <artifactId>flash-ext-web-bundler</artifactId>
                 <version>${project.version}</version>
             </dependency>
+            <dependency>
+                <groupId>dev.relism</groupId>
+                <artifactId>flash-ext-mcp</artifactId>
+                <version>${project.version}</version>
+            </dependency>
             <dependency>
                 <groupId>dev.relism</groupId>
                 <artifactId>fpr-core</artifactId>