refactor: model bin errors as neverthrow Result values (task 0003)

Split the view command out of the entry point and make its failure a
value rather than an exception. index.ts is now scaffolding plus
dispatch; view.ts owns the behaviour, returning Result<string, ViewError>
(a plain-data tagged union) via neverthrow, with try/catch confined to a
readFile adapter. The entry point matches the Result at the boundary.

Because viewFile is a pure in-process function it is now unit-tested
directly (and counted by coverage), while the subprocess tests stay as
the end-to-end check. ADR 0008 records the errors-as-values convention.

packages/bin/package.json

@@ -14,6 +14,7 @@
     "@kitchen-md/core": "workspace:*",
     "chalk": "^5.6.2",
     "commander": "^15.0.0",
+    "neverthrow": "^8.2.0",
     "yaml": "^2.9.0"
   }
 }