test: add a duplicate-tool-names test server for the #1957 repro

Nothing in the repo could serve the shape this fix is about: every preset
registers a unique name, and the SDK's `registerTool` rejects a repeat. So the
only reproduction was a unit test — there was no way to smoke the real app
against a server that returns duplicates.

Adds `ServerConfig.duplicateToolNames` (a list of registered tool names) to the
composable test server, plumbed through the JSON config, and a showcase config
`duplicate-tool-names-http.json`. The named tools are emitted a second time in
`tools/list` with the same `name` and a "(duplicate)" title.

The repeats are appended after the whole list rather than placed beside their
twin. That is both the realistic shape (two tool sources concatenated) and what
makes the defect observable: React matches a leading run of same-key children
first, so a head-adjacent duplicate happens to line up and the bug hides. Only
a separated pair collides in the keyed map and orphans a row — verified both
ways against the prod bundle.

The `tools/list` override is shared with the existing pagination handler (which
already hand-builds the list); with no `maxPageSize` it returns a single
unbounded page. Duplication happens before pagination, so a duplicated pair can
straddle a page boundary the way a real server's would.

Also adds a ToolControls test for this appended ordering, distinct from the
reporter's interleaved fixture, and documents the config in the README showcase
table.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SW1p8E2uiyyLx4RKwrwSrt

test-servers/src/load-config.ts

@@ -66,6 +66,12 @@ export interface ConfigFile {
     resourceTemplates?: number;
     prompts?: number;
   };
+  /**
+   * Names of registered tools to emit **twice** in `tools/list` (same `name`,
+   * the second's title marked "(duplicate)") — the nonconforming-but-real shape
+   * no preset can produce. See {@link ServerConfig.duplicateToolNames} (#1957).
+   */
+  duplicateToolNames?: string[];
   /**
    * Gate a tool's `tools/list` visibility on a client-declared extension. Maps
    * extension id → tool name; the tool appears only when the connected client