feat(cli): add Slack community CTA on errors, crashes, setup, and help (#277)

* feat(cli): show Slack CTA on help and unexpected errors

* feat(cli): show Slack CTA after crashes

* feat(setup): show Slack community note after setup

* chore: refresh Python lockfile versions

packages/cli/test/community-cta.test.ts

@@ -0,0 +1,72 @@
+import { describe, expect, it } from 'vitest';
+
+import {
+  SLACK_HELP_FOOTER,
+  SLACK_SETUP_NOTE,
+  writeErrorCommunityHint,
+} from '../src/community-cta.js';
+import type { KtxCliIo } from '../src/cli-runtime.js';
+
+function makeIo(stderrIsTty: boolean): { io: KtxCliIo; stderr: () => string } {
+  let stderr = '';
+  const stderrStream = stderrIsTty
+    ? {
+        isTTY: true,
+        columns: 80,
+        on: () => undefined,
+        write: (chunk: string) => {
+          stderr += chunk;
+        },
+      }
+    : {
+        write: (chunk: string) => {
+          stderr += chunk;
+        },
+      };
+
+  return {
+    io: {
+      stdout: {
+        write: () => undefined,
+      },
+      stderr: stderrStream,
+    },
+    stderr: () => stderr,
+  };
+}
+
+describe('community CTA', () => {
+  it('writes the error hint to TTY stderr', () => {
+    const testIo = makeIo(true);
+
+    writeErrorCommunityHint(testIo.io, 'error');
+
+    expect(testIo.stderr()).toContain('Stuck? The ktx community can help');
+    expect(testIo.stderr()).toContain('https://ktx.sh/slack');
+  });
+
+  it('suppresses the error hint for non-TTY stderr', () => {
+    const testIo = makeIo(false);
+
+    writeErrorCommunityHint(testIo.io, 'error');
+
+    expect(testIo.stderr()).toBe('');
+  });
+
+  it('uses stronger crash copy for crash hints', () => {
+    const testIo = makeIo(true);
+
+    writeErrorCommunityHint(testIo.io, 'crash');
+
+    expect(testIo.stderr()).toContain('This may be a bug');
+    expect(testIo.stderr()).toContain('https://ktx.sh/slack');
+  });
+
+  it('exports setup and help copy with the stable Slack URL', () => {
+    expect(SLACK_HELP_FOOTER).toBe('Community & support: https://ktx.sh/slack');
+    expect(SLACK_SETUP_NOTE).toEqual({
+      title: 'Community',
+      body: 'Questions or feedback? Join the ktx Slack: https://ktx.sh/slack',
+    });
+  });
+});