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/i18n/en.json

@@ -127,12 +127,40 @@
       "line": "⚡ {{source}} {{frequency}} +{{magnitude}}dB",
       "count": "{{count}} anomalies witnessed this session"
     },
+    "hints": {
+      "wire": "the wire whispers on its own when you listen passively",
+      "evp": "the veil listens through your microphone — grant it your ear",
+      "radio": "a tuner in the hand hears further than the wire",
+      "ouija": "ask below, or let the board drift",
+      "emf": "hold still; the field remembers movement"
+    },
+    "conditions": {
+      "title": "VEIL CONDITIONS",
+      "lit": "{{percent}}% lit",
+      "veil": {
+        "thin": "the veil runs thin tonight",
+        "veiled": "the veil hangs, neither open nor shut",
+        "heavy": "the veil lies heavy"
+      },
+      "fieldQuiet": "field: quiet",
+      "fieldStorm": "geomagnetic storm",
+      "moon": {
+        "new_moon": "new moon",
+        "waxing_crescent": "waxing crescent",
+        "first_quarter": "first quarter",
+        "waxing_gibbous": "waxing gibbous",
+        "full_moon": "full moon",
+        "waning_gibbous": "waning gibbous",
+        "last_quarter": "last quarter",
+        "waning_crescent": "waning crescent"
+      }
+    },
     "evp": {
       "start": "open the microphone",
       "stop": "close the microphone",
       "listening": "listening to the voice band…",
       "deniedTitle": "the microphone stays shut",
-      "denied": "This vessel refused the microphone. Grant audio permission in your browser to practice EVP — or let the Wire Ghost listen instead; it needs nothing but the network you already fear.",
+      "denied": "This vessel refused the microphone. Grant audio permission in your browser's site settings to practice EVP — or turn to the ouija board or the Wire Ghost instead; the board needs no ear, and the wire only the network you already fear.",
       "floor": "room floor",
       "band": "voice band 300–3400 Hz",
       "scopeLabel": "live audio spectrum from the microphone"
@@ -141,7 +169,7 @@
       "start": "sweep the band",
       "stop": "rest the needle",
       "unsupportedTitle": "this vessel cannot hear the radio dead",
-      "unsupported": "Spirit Radio needs Chromium (WebUSB) and an RTL-SDR dongle. The other modes do not — the wire and the microphone still answer.",
+      "unsupported": "Spirit Radio needs Chromium (WebUSB) and an RTL-SDR dongle. The other modes still answer — EVP hears through the microphone you already carry, and the wire needs nothing at all.",
       "troubleshoot": "troubleshooting: chromium-based browser · udev rules for 0bda:2838 · the dongle plugged in, not merely believed in",
       "insecure": "the radio dead only speak through consecrated ground — open this site via its https address.",
       "insecureHint": "localhost counts as hallowed; a bare http://lan-ip does not.",