v0.2.6

The first published release after 0.2.1: it also contains everything listed
under 0.2.2–0.2.5 below, which were not published separately.

No crate changes. Released together with oxframe-cli 0.2.6 (oxframe mcp,
--json, and hints on the compile errors agents hit most often).

The scene API and the editor protocol are unchanged.