refactor(bin): replace process.exit() in CLI entrypoints + ratchet rule to error (#738) (#741)

Part 2 of 2 of the n/no-process-exit cleanup (completes umbrella #738; part 1
was #739/scripts). Converts the 20 flagged process.exit() calls in the three
hand-written gsd-core/bin CLI entrypoints and flips n/no-process-exit to error.

- New src/cli-exit.cts -> gsd-core/bin/lib/cli-exit.cjs (ExitError + runMain),
  the gsd-core-side equivalent of scripts/lib/cli-exit.cjs; registered in
  .gitignore, eslint ignores, and the inventory manifest like its siblings.
- gsd-tools.cjs: 13 apply-prompt-budget exits -> throw ExitError; main()->runMain.
- verify-reapply-patches.cjs: 6 exits -> throw ExitError / return verdict; runMain.
- check-latest-version.cjs: 1 exit -> return verdict; runMain.
- eslint.config.mjs: n/no-process-exit warn -> error.

Scope note: the gsd-core/bin/lib/*.cjs modules (core, state, profile-pipeline,
roadmap-command-router, adr-parser, ui-safety-gate) are tsc-generated and
eslint-ignored (ADR-457), so their process.exit calls were never flagged and are
intentionally left untouched. Only the linted hand-written entrypoints are in scope.

Exit codes verified unchanged for all three entrypoints.

Closes #738

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

src/cli-exit.cts

@@ -0,0 +1,41 @@
+/**
+ * Error carrying a process exit code. CLI logic throws this instead of calling
+ * process.exit() (banned by n/no-process-exit); runMain() translates it into
+ * process.exitCode at the entrypoint.
+ */
+class ExitError extends Error {
+  code: number;
+  hasUserMessage: boolean;
+  constructor(code = 1, message?: string) {
+    super(message === undefined ? `process exit ${code}` : message);
+    this.name = 'ExitError';
+    this.code = code;
+    this.hasUserMessage = message !== undefined;
+  }
+}
+
+/**
+ * Run a CLI main and translate its outcome into process.exitCode (never
+ * process.exit, so n/no-process-exit stays satisfied; output flushes and
+ * process.on('exit') cleanup still fires). main may be sync or async:
+ *   number return -> process.exitCode = it
+ *   thrown ExitError -> process.exitCode = err.code (+ stderr err.message if hasUserMessage && code!=0)
+ *   other throw -> stderr stack + process.exitCode = 1
+ */
+function runMain(main: () => number | void | Promise<number | void>): void {
+  Promise.resolve()
+    .then(() => main())
+    .then((code) => { if (typeof code === 'number') process.exitCode = code; })
+    .catch((err: unknown) => {
+      if (err instanceof ExitError) {
+        if (err.hasUserMessage && err.code !== 0) process.stderr.write(`${err.message}\n`);
+        process.exitCode = err.code;
+        return;
+      }
+      const e = err as Error;
+      process.stderr.write(`${e && e.stack ? e.stack : String(err)}\n`);
+      process.exitCode = 1;
+    });
+}
+
+export = { ExitError, runMain };