feat: legibility wave — veil conditions, first-run hints, kinder errors

Workstream B of the usability wave (#2 hints, #3 conditions, #4 errors):

- GET /api/conditions (new backend/app/routes/conditions.py): composes
  celestial veil_thinness with the cached NOAA Kp reading; lenient lon
  parsing (junk degrades to moon-only, never 422); geomagnetic may be
  null on a cold cache. Route tests stub the cache — no live NOAA calls.
- VeilConditions strip in the séance side column: moon glyph + phase,
  % lit, veil-thinness phrase, Kp line only when data exists. Polls
  every 10 min; renders nothing while loading; no error state.
- ModeHint: per-mode in-fiction one-liner after ~15s idle, suppressed
  once the mode's sensor runs this session, dismissal persisted in
  localStorage (qm_hint_<mode>). One mount line per panel.
- Error copy upgraded to detect-and-redirect: mic denied points at site
  settings and the ouija board/wire; WebUSB-unsupported suggests EVP.
- i18n en/es parity for every new string; coverage-check template
  domains extended for the new template-key call sites.

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

frontend/src/components/VeilConditions.test.tsx

@@ -0,0 +1,50 @@
+import { render, screen, waitFor } from '@testing-library/react'
+import { afterEach, describe, expect, it, vi } from 'vitest'
+import '../i18n'
+import { VeilConditions } from './VeilConditions'
+
+const sky = {
+  moon_phase: 0.5,
+  moon_name: 'full moon',
+  moon_illumination: 0.98,
+  witching_proximity: null,
+  thinness: 0.98,
+}
+
+function stubFetch(body: unknown, ok = true) {
+  vi.stubGlobal(
+    'fetch',
+    vi.fn().mockResolvedValue({ ok, json: () => Promise.resolve(body) }),
+  )
+}
+
+describe('VeilConditions', () => {
+  afterEach(() => {
+    vi.unstubAllGlobals()
+  })
+
+  it('renders moon, thinness phrase and storm line from the endpoint', async () => {
+    stubFetch({ sky, geomagnetic: { kp: 6.3, label: 'moderate geomagnetic storm', storm: true } })
+    render(<VeilConditions />)
+    expect(await screen.findByText('full moon')).toBeInTheDocument()
+    expect(screen.getByText('98% lit')).toBeInTheDocument()
+    expect(screen.getByText('the veil runs thin tonight')).toBeInTheDocument()
+    expect(screen.getByText('geomagnetic storm')).toBeInTheDocument()
+    expect(screen.getByText('Kp 6')).toBeInTheDocument()
+  })
+
+  it('omits the field line when geomagnetic is null', async () => {
+    stubFetch({ sky, geomagnetic: null })
+    render(<VeilConditions />)
+    expect(await screen.findByText('full moon')).toBeInTheDocument()
+    expect(screen.queryByText(/field:/)).toBeNull()
+    expect(screen.queryByText(/Kp/)).toBeNull()
+  })
+
+  it('renders nothing when the fetch fails', async () => {
+    vi.stubGlobal('fetch', vi.fn().mockRejectedValue(new Error('down')))
+    const { container } = render(<VeilConditions />)
+    await waitFor(() => expect(fetch).toHaveBeenCalled())
+    expect(container.firstChild).toBeNull()
+  })
+})