feat: open the door — no sign-in wall, ever

Point and shoot. SeancePage no longer redirects a stranger to /enter; it
silently provisions a wanderer (POST /auth/guest, a real account) and drops
them straight into the séance. The landing CTA goes to /seance
unconditionally. Registering is now what it should always have been: how
you *keep* a codex and unlock device pairing — not the toll to get in.

Details that matter:
- One auto-attempt only, guarded by a ref: survives StrictMode's double
  effect, and a failure (rate limit, offline) doesn't retry forever.
- The loading veil covers provisioning, so there's no flash of an empty
  séance while the account is created.
- If provisioning genuinely fails, it falls back to /enter rather than a
  blank screen — the manual door still exists.
- A returning visitor already holds a cookie, so this never fires for them.

App.test's "sends anonymous visitors to /enter" assertion was inverted to
assert the open door instead — that test encoded the wall we just removed.

Verified live: POST /auth/guest returns wanderer-a6f1 and that cookie
authenticates on /auth/me. 366 frontend tests pass; i18n parity holds.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

frontend/src/App.test.tsx

@@ -52,13 +52,16 @@ describe('App', () => {
     )
   })
 
-  it('sends anonymous visitors to /enter from the séance CTA', async () => {
+  it('takes anonymous visitors straight to the séance, with no sign-in wall', async () => {
+    // The open door: a stranger must reach the séance itself. SeancePage
+    // provisions a wanderer for them on arrival; /enter is an upgrade path
+    // (keep your codex, pair a device), never a gate.
     render(<App />)
     await waitFor(() =>
       expect(screen.getAllByText('QUANTUMANCY').length).toBeGreaterThan(0),
     )
     const cta = screen.getByRole('button', { name: /begin the séance/i })
     await userEvent.click(cta)
-    await waitFor(() => expect(window.location.pathname).toBe('/enter'))
+    await waitFor(() => expect(window.location.pathname).toBe('/seance'))
   })
 })