Demonstrate registration of tools conditioned upon client capability support. Also, obviated need for clientConnected callback to pass sessionId because we defer initial fetching of roots happens when you run the get-roots-list tool.

* In how-it-works.md,
  - added a section on conditional tool registration

* In server/index.ts
  - import registerConditionalTools
  - in an oninitialized handler for the server, call registerConditionalTools
  - removed clientConnected from ServerFactoryResponse and all mentions in docs

* In tools/index.ts
  - export a registerConditionalTools function
  - refactor/move calls to registerGetRootsListTool, registerTriggerElicitationRequestTool, and registerTriggerSamplingRequestTool out of registerTools and into registerConditionalTools

* In server/roots.ts
  - only act if client supports roots
  - remove setInterval from call to requestRoots. It isn't happening during the initialze handshake anymore, so it doesn't interfere with that process if called immediaately

* In get-roots-list.ts, trigger-elicitation-request.ts, and trigger-sampling-request.ts,
  - only register tool if client supports capability

* Throughout the rest of the files, removing all references to `clientConnected`

src/everything/transports/streamableHttp.ts

@@ -38,7 +38,7 @@ app.post("/mcp", async (req: Request, res: Response) => {
       // Reuse existing transport
       transport = transports.get(sessionId)!;
     } else if (!sessionId) {
-      const { server, clientConnected, cleanup } = createServer();
+      const { server, cleanup } = createServer();
 
       // New initialization request
       const eventStore = new InMemoryEventStore();
@@ -68,7 +68,6 @@ app.post("/mcp", async (req: Request, res: Response) => {
       // Connect the transport to the MCP server BEFORE handling the request
       // so responses can flow back through the same transport
       await server.connect(transport);
-      clientConnected(transport.sessionId);
       await transport.handleRequest(req, res);
       return;
     } else {