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/src/index.ts

@@ -1,8 +1,6 @@
 #!/usr/bin/env bun
-import { readFileSync } from "node:fs";
-import { parse } from "@kitchen-md/core";
 import { Command } from "commander";
-import { render } from "./render.ts";
+import { formatViewError, viewFile } from "./view.ts";
 
 const program = new Command();
 
@@ -13,15 +11,13 @@ program
   .description("Render a Recipe File to the terminal")
   .argument("<file>", "path to a Recipe File")
   .action((file: string) => {
-    let content: string;
-    try {
-      content = readFileSync(file, "utf8");
-    } catch (error) {
-      const reason = error instanceof Error ? error.message : String(error);
-      process.stderr.write(`kitchen: cannot read '${file}': ${reason}\n`);
-      process.exit(1);
-    }
-    process.stdout.write(render(parse(content)));
+    viewFile(file).match(
+      (output) => process.stdout.write(output),
+      (error) => {
+        process.stderr.write(`kitchen: ${formatViewError(error)}\n`);
+        process.exit(1);
+      },
+    );
   });
 
 program.parse();