terraphim-clients v1.21.4

Patch release for signed terraphim-grep updater assets.\n\nChanges:\n- Preserves the release asset filename during updater downloads so zipsign verifies against the same context used for signing.\n- Retains the Terraphim Clients zipsign Release Key 2026-07 verifier introduced in v1.21.3.\n- Bumps terraphim-grep workspace version to 1.21.4.\n- Attaches signed macOS ARM64 terraphim-grep archive.\n\nCompatibility note:\n- Updating directly from v1.21.2 with the old embedded verifier key is not supported because the old private signing key is unavailable in usable zipsign form. Install v1.21.4 manually once; future signed updates can use this verifier and filename-preserving updater path.\n\nAsset SHA-256:\n- terraphim-grep-1.21.4-aarch64-apple-darwin.tar.gz: 49d20d65ea8a1cb478dd6e12095634f340f09956533e3222ac53776ca3501a52