feat: thread step --count/-c <number> to run multiple steps

Add --count/-c flag to 'uwf thread step' for running N steps in one
invocation, stopping early if $END is reached.

- cmdThreadStep now loops up to count times, delegates to cmdThreadStepOnce
- CLI parses -c/--count, defaults to 1 (backward compatible single output)
- Validation rejects 0, negative, and non-integer counts
- 7 new tests covering CLI parsing and count validation

Fixes #373

Co-authored-by: uwf-hermes (solve-issue workflow)

packages/cli-workflow/src/commands/thread.ts

@@ -673,6 +673,27 @@ export async function cmdThreadStep(
   storageRoot: string,
   threadId: ThreadId,
   agentOverride: string | null,
+  count: number,
+): Promise<StepOutput[]> {
+  if (count < 1 || !Number.isInteger(count)) {
+    fail(`--count must be a positive integer, got: ${count}`);
+  }
+
+  const results: StepOutput[] = [];
+  for (let i = 0; i < count; i++) {
+    const result = await cmdThreadStepOnce(storageRoot, threadId, agentOverride);
+    results.push(result);
+    if (result.done) {
+      break;
+    }
+  }
+  return results;
+}
+
+async function cmdThreadStepOnce(
+  storageRoot: string,
+  threadId: ThreadId,
+  agentOverride: string | null,
 ): Promise<StepOutput> {
   const index = await loadThreadsIndex(storageRoot);
   const headHash = index[threadId];