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.css

@@ -0,0 +1,54 @@
+/* VeilConditions — compact sky/field strip in the séance side column.
+   Tokens follow SeancePage.css: phosphor #7cffb2 · violet #b26bff ·
+   panel rgba(16,16,26,0.85) · border rgba(124,255,178,0.18). */
+
+.veil-conditions {
+  padding: 0.6rem 0.7rem;
+  border: 1px solid rgba(124, 255, 178, 0.18);
+  border-radius: 4px;
+  background: rgba(16, 16, 26, 0.85);
+  font-size: 0.76rem;
+  line-height: 1.5;
+  color: #d3e9db;
+}
+
+.veil-conditions-title {
+  margin: 0 0 0.35rem;
+  font-size: 0.68rem;
+  font-weight: 400;
+  letter-spacing: 0.18em;
+  color: #7cffb2;
+  opacity: 0.7;
+}
+
+.veil-conditions-line {
+  display: flex;
+  align-items: baseline;
+  gap: 0.5rem;
+  min-width: 0;
+  flex-wrap: wrap; /* stays legible at 390px */
+}
+
+.veil-moon-glyph {
+  flex: none;
+  filter: drop-shadow(0 0 4px rgba(178, 107, 255, 0.5));
+}
+
+.veil-moon-name {
+  min-width: 0;
+}
+
+.veil-thinness {
+  color: #b26bff;
+  font-style: italic;
+  opacity: 0.9;
+}
+
+.veil-field-quiet {
+  opacity: 0.75;
+}
+
+.veil-field-storm {
+  color: #b26bff;
+  text-shadow: 0 0 8px rgba(178, 107, 255, 0.6);
+}