feat(deps): type-fest installed for opportunistic utility-type adoption

Dev-only — ships zero runtime. Adds 150+ named utility types
(SetRequired, PartialDeep, MergeDeep, Promisable, Jsonifiable,
etc.). Adopt at call sites when a hand-rolled Omit<X, Y> & Pick<Z, W>
composition would read more clearly with a named util.

No forced migration: the codebase only has 3 small hand-rolled
compositions today, all readable as-is.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

package.json

@@ -150,6 +150,7 @@
     "react-grab": "^0.1.34",
     "tailwindcss": "^4.3.0",
     "tsx": "^4.21.0",
+    "type-fest": "^5.6.0",
     "typescript": "^6.0.3",
     "vitest": "^4.1.6"
   },