v0.6.0 — remove demo runtime

Removes the Demo runtime entirely (the in-process, zero-cost no-op runtime built for public demo sites). The Create-Agent dropdown no longer offers it, and the adapter / registry / model-discovery entries are gone.

The 7 runtimes — claude, codex, copilot, opencode, kimi, pi, cursor — are unchanged.

Self-hosters: run npx @fancyboi999/open-tag-daemon@latest (or @0.6.0) and restart your daemon to drop the demo runtime. (#112)