feat: Phase 5+6 Aether Drift — legacy token removal, colorful avatars & Backspace branding

Phase 5: Remove all 54 legacy Discord token definitions from tailwind.config.js,
migrate body classes in index.html to Aether Drift tokens, update ARCHITECTURE_AUDIT.md.

Phase 6: Replace flat purple fallback avatars with deterministic colorful gradients
(mint, sky, lavender, coral, rose, teal, amber) based on user/server ID hash.
Replace Discord logo SVG with Backspace "B" in server strip. Add per-server gradient
icons with hover glow. Update profile popout banner and incoming call modal to match.

packages/web/tailwind.config.js

@@ -7,61 +7,6 @@ export default {
   theme: {
     extend: {
       colors: {
-        // ── LEGACY (preserved until Phase 5 removal) ──
-        discord: {
-          // Backgrounds (darkest → lightest) — Discord "Dark" theme
-          'bg-floating':       '#080a0b',
-          'bg-tertiary':       '#111214',
-          'bg-server':         '#111214',
-          'bg-user-area':      '#1a1b1e',
-          'bg-secondary':      '#1e1f22',
-          'bg-members':        '#1e1f22',
-          'bg-home':           '#1a1d20',
-          'bg-hover':          '#232428',
-          'bg-primary':        '#232428',
-          'bg-input':          '#2b2d31',
-          'bg-surface':        '#2b2d31',
-          'bg-surface-higher': '#313338',
-          'bg-active':         '#313338',
-          'bg-accent':         '#353840',
-          'bg-overlay':        'rgba(0, 0, 0, 0.90)',
-
-          // Text
-          'text-primary':   '#ffffff',
-          'text-normal':    '#dcdcdf',
-          'text-secondary': '#c5c6ca',
-          'text-muted':     '#abacb2',
-          'text-header':    '#ffffff',
-          'text-link':      '#76aff6',
-          'text-positive':  '#73c48b',
-          'text-warning':   '#faa900',
-          'text-danger':    '#ff938e',
-
-          // Channel/Interactive
-          'channels-default':  '#999aa1',
-          'interactive-muted': '#4e5058',
-
-          // Brand
-          'blurple':        '#5865f2',
-          'blurple-hover':  '#4452bb',
-          'blurple-active': '#3a48a3',
-
-          // Status
-          'green':      '#23a55a',
-          'yellow':     '#f0b232',
-          'red':        '#f23f43',
-          'red-hover':  '#a9232e',
-
-          // Notification badge
-          'notification': '#da3e44',
-
-          // Modifiers (semi-transparent — works on any background)
-          'modifier-hover':    'rgba(255,255,255,0.08)',
-          'modifier-active':   'rgba(255,255,255,0.16)',
-          'modifier-selected': 'rgba(255,255,255,0.20)',
-          'modifier-accent':   'rgba(255,255,255,0.12)',
-        },
-
         // ── AETHER DRIFT TOKENS ──
         surface: {
           base:     'var(--bg-base)',