design: align visual style with bincio_autarchive

- Add src/theme.ts with centralised color palette
- Backgrounds: #111 → #09090b, surfaces #1e1e1e → #18181b
- All cards get 1px #27272a borders (matches autarchive cards)
- Text: #fff/#888/#555 → #f4f4f5/#a1a1aa/#71717a
- Accent: #3b82f6 → #60a5fa (autarchive default palette)
- Tab icons: colored emoji → monochromatic Unicode (◉ ☰ ⚙)
- Action buttons use muted palette (#16a34a / #d97706 / #dc2626)
- Keep-awake toggle uses ◑/◌ symbols, border highlights accent on active
- Connect/Scan buttons match autarchive surface+border style

src/theme.ts

@@ -0,0 +1,24 @@
+export const colors = {
+  bg:           '#09090b',
+  surface:      '#18181b',
+  border:       '#27272a',
+  borderStrong: '#3f3f46',
+
+  text:         '#f4f4f5',
+  textSub:      '#a1a1aa',
+  textMuted:    '#71717a',
+  placeholder:  '#52525b',
+
+  accent:       '#60a5fa',
+  accentDim:    'rgba(96,165,250,0.15)',
+
+  success:      '#86efac',
+  successBg:    '#14532d',
+  error:        '#fca5a5',
+  errorBg:      '#7f1d1d',
+
+  // recording action buttons
+  btnStart:     '#16a34a',
+  btnPause:     '#d97706',
+  btnStop:      '#dc2626',
+} as const;