fix(app): keep exported widget scripts separate

[asasemahmed]

The standalone HTML export joins jsFunctions and every jsExpressions entry with "\n" into one script. The live sandbox runs each piece as its own script, so generated code often has no trailing semicolons. Once joined, automatic semicolon insertion merges the pieces, and an exported widget that worked live is dead after "Download" or "Copy". Two examples:

• jsFunctions: "let count = 0" followed by the async IIFE becomes 0(async () => ...), which throws TypeError: 0 is not a function.
• Expressions draw() and [1, 2].forEach(...) become draw()[1, 2].forEach(...).

The pieces are now joined with "\n;\n", so each stays its own statement.

Tests: export-utils.test.ts runs the exported script with semicolon-free pieces and checks that every expression ran.