Add EMF field mode, Armory shop/waitlist, and ambient haunting layer

Three self-contained features, verified complete and cross-wired
end-to-end (audited: backend 54/54 tests, frontend 110/110 tests,
tsc --noEmit clean, i18n coverage script clean):

- EMF mode: DeviceMotion/DeviceOrientation-based field-meter sensing,
  a fifth séance channel alongside Wire/EVP/Radio/Ouija, with its own
  fragment prompt persona and full frontend gauge UI.
- Armory (shop/waitlist): pre-order capture page for the future
  Ultimate Quantum Box hardware line, rate-limited public endpoint,
  explicitly no payment collection.
- Haunting layer: ambient possession effects (dread-bed audio, title
  glitching, idle-paced whispers/manifests), respects
  prefers-reduced-motion, mounted once at the app root.

Plus WebUSB robustness fixes in lib/sdr.ts (Terratec vendor ID,
explicit selectConfiguration, isSecureContext gate).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013PphXq1s43DNRj1uWKGXof

frontend/src/pages/SeancePage.css

@@ -749,14 +749,16 @@
 .evp-panel,
 .radio-panel,
 .ouija-panel,
-.wire-panel {
+.wire-panel,
+.emf-panel {
   display: flex;
   flex-direction: column;
   gap: 0.55rem;
 }
 
 .evp-scope,
-.radio-waterfall {
+.radio-waterfall,
+.emf-gauge {
   width: 100%;
   border: 1px solid rgba(124, 255, 178, 0.18);
   border-radius: 4px;
@@ -772,8 +774,13 @@
   height: 110px;
 }
 
+.emf-gauge {
+  height: 140px;
+}
+
 .evp-readout,
-.radio-readout {
+.radio-readout,
+.emf-readout {
   display: flex;
   justify-content: space-between;
   align-items: baseline;
@@ -798,6 +805,70 @@
   color: rgba(211, 233, 219, 0.75);
 }
 
+/* emf */
+.emf-level {
+  color: #7cffb2;
+  font-size: 1.5rem;
+  text-shadow: 0 0 14px rgba(124, 255, 178, 0.65);
+  font-variant-numeric: tabular-nums;
+}
+
+.emf-baseline {
+  font-size: 0.72rem;
+  letter-spacing: 0.08em;
+  font-variant-numeric: tabular-nums;
+}
+
+.emf-listening {
+  margin: 0;
+  display: flex;
+  align-items: center;
+  gap: 0.5rem;
+  font-size: 0.76rem;
+  color: rgba(211, 233, 219, 0.75);
+}
+
+.emf-actions {
+  display: flex;
+  align-items: center;
+  gap: 0.6rem;
+  margin-top: 0.7rem;
+}
+
+.emf-actions .panel-action {
+  margin-top: 0;
+}
+
+/* smaller secondary control (calibrate, try again) */
+.panel-subaction {
+  align-self: flex-start;
+  background: transparent;
+  border: 1px solid rgba(124, 255, 178, 0.3);
+  border-radius: 3px;
+  color: rgba(124, 255, 178, 0.75);
+  font-family: 'IBM Plex Mono', monospace;
+  font-size: 0.7rem;
+  letter-spacing: 0.12em;
+  text-transform: uppercase;
+  padding: 0.32rem 0.7rem;
+  cursor: pointer;
+  transition: box-shadow 150ms ease, color 150ms ease;
+}
+
+.panel-subaction:hover:not(:disabled) {
+  color: #7cffb2;
+  box-shadow: 0 0 10px rgba(124, 255, 178, 0.25);
+}
+
+.panel-subaction:disabled {
+  opacity: 0.35;
+  cursor: not-allowed;
+}
+
+.panel-notice .panel-subaction {
+  margin-top: 0.2rem;
+}
+
 .rec-dot {
   width: 8px;
   height: 8px;