Why: CLI's offline settings writes need AGENT_CATALOG_SCHEMA_VERSION but
cannot import from out/main (electron-vite removes it during rebuild).
Extract pure schema logic to src/shared, FS-bound backup operations to
src/main. Add CLI require-resolution verification to catch MODULE_NOT_FOUND
at build time instead of runtime. Fix hydration-time purge to defer
incomplete repos: was deleting all local owners on remote-only hydration
(incident 2026-07-19).
