🐛 Gate the universe to finite, literal keys

An open universe (`string`, `number`, a template literal) makes the
handler map index-like, so a partial object satisfied the exhaustive
overload and the runtime `dispatch` throw was reachable. A universe
containing a member and its stringification (`"true" | true`, `1 | "1"`)
collapsed two members onto one key.

- reject broad universes and value/stringification collisions at the
  factory, with a diagnostic naming the reason
- invert `PatternKey` against the universe (`Member<T, K>`) instead of
  `PatternParam<K>`, so a standalone `"true"` is typed `"true"`
- intersect `UniverseGate<T>` into the handler and fallback parameters,
  preserving `R` inference and the popup

cspell.json

@@ -43,7 +43,9 @@
         "silverwind",
         "idris",
         "todotasks",
-        "connor"
+        "connor",
+        "injective",
+        "injectivity"
     ],
     "ignorePaths": ["dist", "node_modules", "coverage", "*.svg", ".gitignore"]
 }