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/WorkspaceChatWidget.vue

@@ -3,6 +3,7 @@ import { ref, computed, nextTick, onMounted, onUnmounted, watch } from 'vue';
 import { useChatStore } from '@/stores/chat';
 import ChatPanel from '@/components/ChatPanel.vue';
 import ChatInputBar from '@/components/ChatInputBar.vue';
+import { RotateCcw, ChevronDown, ChevronUp } from 'lucide-vue-next';
 
 const props = defineProps<{ projectId: number }>();
 
@@ -195,11 +196,11 @@ defineExpose({ prefill });
             </button>
           </div>
         </div>
-        <button class="btn-icon-sm" title="Restart conversation" @click="restart">↻</button>
+        <button class="btn-icon-sm" title="Restart conversation" @click="restart">
+          <RotateCcw :size="16" />
+        </button>
         <button class="btn-icon-sm" title="Collapse" @click="collapse">
-          <svg width="12" height="12" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2.5">
-            <polyline points="6 9 12 15 18 9"/>
-          </svg>
+          <ChevronDown :size="16" />
         </button>
       </div>
     </div>
@@ -217,9 +218,7 @@ defineExpose({ prefill });
     <!-- Collapsed: standalone input bar with expand affordance -->
     <div v-else class="ws-chat-collapsed">
       <button class="ws-chat-expand-btn" title="Expand chat" @click="expand">
-        <svg width="14" height="14" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2.5">
-          <polyline points="18 15 12 9 6 15"/>
-        </svg>
+        <ChevronUp :size="16" />
       </button>
       <div class="ws-chat-input-row">
         <ChatInputBar