fix(tauri-release): stage AppImage repair release set

[ElbertePlinio]

Summary

• stage rebuilt AppImage bytes, updater signature, and patched feed before touching live release files
• verify the staged release set, then commit artifact → signature → feed with a rollback journal
• preserve unsigned stale-signature behavior at commit time and cover modes, symlinks, compression, signing modes, malformed/stable/nightly feeds, tool failures, and every commit boundary

Validation

• bun run typecheck
• bun run test (362 passed)
• bun run build
• serious local release-infrastructure review: clean after targeted fix verification

Refs #37 — CAND-5 only.