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>

pnpm-lock.yaml

@@ -371,6 +371,9 @@ importers:
       tsx:
         specifier: ^4.21.0
         version: 4.21.0
+      type-fest:
+        specifier: ^5.6.0
+        version: 5.6.0
       typescript:
         specifier: ^6.0.3
         version: 6.0.3