feat(design): surface phase PR 1 — Lucide icon migration + scale enforcement

Replaces every hand-inlined SVG in the chrome (60 across 15 files)
with Lucide components. Snaps icon sizes to the doc's 16/24 scale —
all icons in this pass land at 16. AppLogo wordmark stays as the
legitimate "custom app icon" exception per the doc; GraphView's <svg>
mount point for D3 stays as well.

Replaces emoji-as-icons in clear button-affordance cases with their
Lucide equivalents: ✕ → X (close/dismiss buttons across 8 files), ✓ →
Check (ProjectView task-advance button), 🎤 → Mic (ChatPanel voice
CTA), 📎 → Paperclip (ChatView context toggle), &uarr; → ArrowUp
(ChatInputBar Send), &times; → X (ChatPanel context-note remove), ☀/☾
→ Sun/Moon (AppHeader theme toggle).

Inline emoji punctuation in textual confirmation copy ("Saved ✓",
"Created ✓", `done: "✓"` status maps, `'✓' : '📄'` interpolations)
is left for surface-phase voice/tone touchups — replacing requires
structural template changes and is best done per-component.

Stroke weight stays at Lucide's default 2px; tightening to the doc's
1.5/1 is deferred per the surface-phase spec (option ii: drop-in +
scale enforcement).

Adds lucide-vue-next ^0.469.0 to frontend/package.json. Docker
rebuild handles the install.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/components/NotificationsPanel.vue

@@ -1,4 +1,5 @@
 <script setup lang="ts">
+import { X } from "lucide-vue-next";
 import { onMounted } from 'vue'
 import { useRouter } from 'vue-router'
 import { useNotificationsStore } from '@/stores/notifications'
@@ -56,7 +57,7 @@ onMounted(() => store.fetchAll())
           </p>
           <span class="notif-time">{{ relativeTime(n.created_at) }}</span>
         </div>
-        <button class="btn-notif-close" @click.stop="store.markRead(n.id)" aria-label="Dismiss">✕</button>
+        <button class="btn-notif-close" @click.stop="store.markRead(n.id)" aria-label="Dismiss"><X :size="16" /></button>
       </li>
     </ul>
     <div v-else class="notif-empty">No unread notifications</div>