ui(icons): replace colored emoji with modern single-color line icons (lucide-vue-next)

Add lucide-vue-next (stroke-based, single-color, currentColor) and swap emoji icons
across nav + all main views: Settings/LogOut (App), BarChart3/Users/Plus (Analytics),
LayoutDashboard (MyBoard), Sparkles/Users/Pencil (GroupEdit), Box/ListChecks/Paperclip/
PlusCircle/ArrowLeft (GroupBuilder), Target/ArrowLeft/Search (Chat/Personas/Training),
User/Lock/Globe (Settings), Users/UserPlus/Info (AdminUsers).
- Buttons become inline-flex for icon+text alignment.
- Icons inherit currentColor (single color, modern line style).
- Rebuild dist with lucide.

frontend/dist/assets/Chat-Dq49zqgJ.css

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+.thread[data-v-b21475ac]{background:#eceff4;border:1px solid var(--border);border-radius:var(--radius);padding:16px;min-height:320px;max-height:52vh;overflow-y:auto;display:flex;flex-direction:column;gap:8px}.bubble[data-v-b21475ac]{max-width:72%;padding:10px 14px;white-space:pre-wrap;word-break:break-word}.composer[data-v-b21475ac]{display:flex;gap:8px;margin-top:12px}.task[data-v-b21475ac]{margin-bottom:12px;background:#fff7ed;border-color:#fed7aa}.debrief[data-v-b21475ac]{margin-top:16px}.json[data-v-b21475ac]{background:#0f172a;color:#9ca3af;padding:10px;border-radius:8px;font-size:11px;overflow:auto;max-height:260px}button.danger[data-v-b21475ac]{background:var(--red);color:#fff;border:none}.guide[data-v-b21475ac]{background:#eef2ff;border-color:#c7d2fe;margin-bottom:12px}.reveal-grid[data-v-b21475ac]{display:grid;grid-template-columns:1fr 1fr;gap:8px;margin-top:8px}.rev[data-v-b21475ac]{display:flex;flex-direction:column;background:#f8fafc;border:1px solid var(--border);border-radius:8px;padding:8px 10px}.rk[data-v-b21475ac]{font-size:12px;color:var(--muted)}.rv[data-v-b21475ac]{font-size:13px;color:var(--ink);margin-top:2px}@media (max-width: 640px){.reveal-grid[data-v-b21475ac]{grid-template-columns:1fr}}