Adds Grounding, Reasoning-Modelle, Token/Parameter examples, an
autocomplete mini-game, and a Copilot agent-building walkthrough with
a live chat-demo payoff. Adds Sprecher.md with per-slide speaker
cards. Fixes malformed data-def attributes and stray baked-in
active/visible classes left over from in-browser edit-mode sessions,
and stops the local save-in-place backups from being tracked.
