docs: clarify audience in 'Why does MCP matter?' bullets

The AI applications bullet mentioned the end-user experience and the
end-users bullet described AI applications, so the two read as swapped
(#3292). Reword both bullets to name their audience directly in every
doc version that carried the identical text.

Fixes #3292

Co-Authored-By: Claude <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ti1NPmKtsCq8aXah341HAp