appEvents schema standardization (fleet, mirror of MARS-411)

Mirror MARS-411 in venus: single log(entry) API, level-as-data, promote hot appEvents fields to real columns, jsonb only for irregular data. DESIGN-FIRST — no build until the fleet column contract is agreed + Elazar sees scope. Venus reconcile notes: (a) adapt onto live Supabase appEvents (uuid pk, timestamptz, camelCase) — no SQLite table; (b) 'no wrappers' targets the logError/logWarn/logInfo helpers MARS-408 shipped — collapse into one log({level,...}); confirm intent before ripping out. Venus caveat: appEvents actively written this session (VENUS-176 toast beacon live v0.89.x category='toast', C-class guard retrofit in flight) — column contract must precede any venus writer retrofit to avoid collision.