chore(slack): remove dead invite path, archive checkSlackJoins poller

Wave-based onboarding makes the auto-invite + polling path obsolete.

- Removes SlackService.inviteUserToSlack — admins now send invites
  through Slack's UI and flip the flag in our admin endpoint.
- Removes the slack_invite_failed admin alert + its detector. The
  alert no longer has a meaningful trigger (we don't attempt invites).
- Archives server/utils/checkSlackJoins.js (and its test) under
  _archive/ in case the polling pattern is needed again post-pilot.
- Deletes the Nitro plugin that scheduled checkSlackJoins on boot
  + hourly. Nothing in nitro.config / nuxt.config / package.json
  registered it elsewhere.
- Drops the slack_invite_failed branch from adminAlerts.test; the
  enum slug stays in adminAlertDismissal so historical dismissal
  rows continue to validate.

notifyNewMember (vetting-channel notification) and findUserByEmail
(used by the auto-flag helper) are retained.

e2e/wave-slack-onboarding.spec.js

@@ -0,0 +1,103 @@
+// Spec: docs/specs/wave-based-slack-onboarding.md
+// Test plan: docs/specs/wave-based-slack-onboarding-tests.md §6 + §7
+//
+// SCAFFOLD: every test is `.skip`ed and contains a TODO. As the UI lands,
+// unskip and fill in selectors / fixtures.
+//
+// These cover the rendered behavior that unit tests can't: dashboard line
+// visibility under different member statuses, and the admin-list "Mark as
+// Slack invited" button + status display.
+
+import { test, expect } from './helpers/fixtures.js'
+
+test.describe('Member dashboard — Slack-coming note (§7)', () => {
+  test.skip('shows note for active member without Slack (7.1)', async () => {
+    // TODO: seed a member { status: 'active', slackInvited: false }, sign in,
+    // navigate to /member/dashboard, assert the one-liner is visible:
+    //   await expect(page.getByText(/within 2.3 weeks/i)).toBeVisible()
+  })
+
+  test.skip('hides note once slackInvited:true (7.2)', async () => {
+    // TODO: same as 7.1 but with slackInvited:true; assert text not present.
+  })
+
+  test.skip('hides note for pending_payment member (7.3)', async () => {
+    // TODO: pending_payment + slackInvited:false; assert text not present.
+  })
+
+  test.skip('hides note for suspended/cancelled/guest (7.4)', async () => {
+    // TODO: parameterize across statuses { suspended, cancelled, guest }.
+  })
+
+  test.skip('copy contains no wave/cohort/batch language (7.5)', async ({ adminPage }) => {
+    await adminPage.goto('/member/dashboard')
+    const html = await adminPage.content()
+    expect(html).not.toMatch(/\bwave\b/i)
+    expect(html).not.toMatch(/\bcohort\b/i)
+    expect(html).not.toMatch(/\bbatch\b/i)
+  })
+
+  test.skip('renders as plain text — no banner / modal / callout styling (7.6)', async () => {
+    // TODO: assert the note's container is not a UAlert / modal / heavy callout
+    // (e.g. no .alert, no role="dialog" wrapper).
+  })
+
+  test.skip('SSR renders without auth — note absent (7.7)', async ({ browser }) => {
+    const context = await browser.newContext()
+    const page = await context.newPage()
+    const response = await page.goto('/member/dashboard')
+    const ssrHtml = await response.text()
+    expect(ssrHtml).not.toMatch(/within 2.3 weeks/i)
+    await context.close()
+  })
+
+  test.skip('copy matches approved wording (7.8)', async () => {
+    // TODO: replace with the final approved string once the Open Question is resolved.
+  })
+})
+
+test.describe('Admin members — Slack-invited control (§6)', () => {
+  test.skip('shows "Mark as Slack invited" for slackInvited:false (6.1)', async ({ adminPage }) => {
+    await adminPage.goto('/admin/members')
+    // TODO: locate a row for a member with slackInvited:false and assert the
+    // button is visible.
+    // await expect(adminPage.getByRole('button', { name: /Mark as Slack invited/i })).toBeVisible()
+  })
+
+  test.skip('replaces button with "Invited <date>" once flipped (6.2)', async () => {
+    // TODO: click the button on a row; assert button is gone, date string visible.
+  })
+
+  test.skip('click triggers single PATCH and updates row in place (6.4)', async ({ adminPage }) => {
+    // TODO: spy on network for /api/admin/members/*/slack-status; click button;
+    // assert single PATCH, success, no full-page reload.
+  })
+
+  test.skip('status labels read "Not yet invited" / "Invited" — not "Pending" (6.5)', async ({ adminPage }) => {
+    await adminPage.goto('/admin/members')
+    // TODO:
+    // await expect(adminPage.getByText(/Not yet invited/i).first()).toBeVisible()
+    // const html = await adminPage.content()
+    // expect(html).not.toMatch(/Slack:\s*Pending/i)
+  })
+
+  test.skip('member detail page mirrors list controls (6.6)', async () => {
+    // TODO: navigate to /admin/members/<id>; assert button + date display.
+  })
+
+  test.skip('no UI references slackInviteStatus (6.7)', async ({ adminPage }) => {
+    // Static assertion of rendered HTML — no leftover badge labels keyed off the dropped field.
+    await adminPage.goto('/admin/members')
+    const html = await adminPage.content()
+    expect(html).not.toMatch(/slackInviteStatus/)
+  })
+
+  test.skip('UI rolls back on PATCH error — no false "Invited" badge (6.8)', async () => {
+    // TODO: mock the endpoint to return 500; assert the row stays in
+    // "Not yet invited" state.
+  })
+
+  test.skip('proposed: sortable on slackInvitedAt + filter "no Slack yet" (6.9)', async () => {
+    // TODO: dependent on Open Question — wire up if implemented.
+  })
+})