Cut version 0.2.21 (current = v_0_2_21) with the adjudicated DO-item fixes.
Also commits the previously-untracked v_0_2_* version files that
versions/index.ts imports (ROADMAP item D2), so a fresh checkout builds
without dangling imports. The missing v_0_2_2 is intentional (versions are
an unordered set).
Built and verified: ten31portal_x86_64.s9pk packs cleanly at 0.2.21:0,
arch x86_64, SDK 0.4.0.
