feat(memory): expose knowledge graph as MCP Resource (#3323)

* feat(memory): expose knowledge graph as MCP Resource

Register the knowledge graph as a readable MCP Resource at
memory://knowledge-graph, enabling clients to discover and read
the graph via the Resources protocol without invoking a tool.

Mutation tools (create_entities, create_relations, add_observations,
delete_entities, delete_observations, delete_relations) now emit
notifications/resources/updated so subscribed clients see live
graph changes.

Resource registration is extracted into the exported
registerKnowledgeGraphResource() function so it can be unit-tested
in isolation, mirroring the everything server's registration
pattern. New tests assert registerResource is called with the
correct kebab-case name, URI, mime type, and that the handler
returns the graph as JSON in the contents array.

Addresses PR #3323 review feedback:
- kebab-case resource name per CLAUDE.md style guide
- single-line comment per CLAUDE.md style guide
- title metadata for client discoverability
- resource update notifications after mutations
- test coverage matching everything/registrations.test.ts pattern
- README documents the new Resource

* feat(memory): support resources/subscribe for the knowledge-graph resource

PR #3323 emitted notifications/resources/updated after every mutation but
the server only advertised resources.listChanged, so resources/subscribe
returned -32601 and a spec-compliant client could never actually subscribe.

Declare resources.subscribe, add subscribe/unsubscribe request handlers that
track subscribed URIs, and only emit notifications/resources/updated when the
client has subscribed to that URI.

Co-authored-by: Lazreg Raed <lazregraed222@gmail.com>

---------

Co-authored-by: olaservo <olahungerford@gmail.com>

src/memory/README.md

@@ -125,6 +125,14 @@ Example:
     - Relations between requested entities
   - Silently skips non-existent nodes
 
+### Resources
+
+- **knowledge-graph** (`memory://knowledge-graph`)
+  - The full knowledge graph as a readable MCP Resource
+  - MIME type: `application/json`
+  - Returns the same shape as `read_graph` (entities and relations)
+  - Mutation tools (`create_entities`, `create_relations`, `add_observations`, `delete_entities`, `delete_observations`, `delete_relations`) emit `notifications/resources/updated` for this URI, so subscribed clients see live changes
+
 # Usage with Claude Desktop
 
 ### Setup