Remove MCP tab and per-project MCP UI from frontend

Claude Code manages MCP natively now (`claude mcp add/list/remove`,
`.mcp.json`, `/mcp`), so Triple-C's own MCP server library is redundant.

Deletes components/mcp/, hooks/useMcpServers.ts, the MCP sidebar tab and
rail icon, the per-project enable checkboxes on ProjectCard, the
mcpServers slice of the Zustand store, the four IPC wrappers, and the
McpServer/McpTransportType types.

Rust backend is untouched in this commit; the commands simply become
unreachable. Backend removal and the legacy container/network cleanup
follow separately.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

app/src/hooks/useMcpServers.ts

@@ -1,55 +0,0 @@
-import { useCallback } from "react";
-import { useShallow } from "zustand/react/shallow";
-import { useAppState } from "../store/appState";
-import * as commands from "../lib/tauri-commands";
-import type { McpServer } from "../lib/types";
-
-export function useMcpServers() {
-  const {
-    mcpServers,
-    setMcpServers,
-    updateMcpServerInList,
-    removeMcpServerFromList,
-  } = useAppState(
-    useShallow(s => ({
-      mcpServers: s.mcpServers,
-      setMcpServers: s.setMcpServers,
-      updateMcpServerInList: s.updateMcpServerInList,
-      removeMcpServerFromList: s.removeMcpServerFromList,
-    }))
-  );
-
-  const refresh = useCallback(async () => {
-    const list = await commands.listMcpServers();
-    setMcpServers(list);
-  }, [setMcpServers]);
-
-  const add = useCallback(
-    async (name: string) => {
-      const server = await commands.addMcpServer(name);
-      const list = await commands.listMcpServers();
-      setMcpServers(list);
-      return server;
-    },
-    [setMcpServers],
-  );
-
-  const update = useCallback(
-    async (server: McpServer) => {
-      const updated = await commands.updateMcpServer(server);
-      updateMcpServerInList(updated);
-      return updated;
-    },
-    [updateMcpServerInList],
-  );
-
-  const remove = useCallback(
-    async (id: string) => {
-      await commands.removeMcpServer(id);
-      removeMcpServerFromList(id);
-    },
-    [removeMcpServerFromList],
-  );
-
-  return { mcpServers, refresh, add, update, remove };
-}