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/AppHeader.vue

@@ -7,6 +7,7 @@ import { useAuthStore } from "@/stores/auth";
 import { useChatStore } from "@/stores/chat";
 import AppLogo from "@/components/AppLogo.vue";
 import NotificationBell from "@/components/NotificationBell.vue";
+import { Sun, Moon, Settings } from "lucide-vue-next";
 
 const { theme, toggleTheme } = useTheme();
 const { toggleShortcuts } = useShortcuts();
@@ -94,15 +95,13 @@ router.afterEach(() => {
         <button class="btn-icon" @click="toggleShortcuts" title="Keyboard shortcuts (?)">?</button>
 
         <button class="btn-icon" @click="toggleTheme" :title="`Switch to ${theme === 'dark' ? 'light' : 'dark'} mode`">
-          {{ theme === "dark" ? "\u2600" : "\u263E" }}
+          <Sun v-if="theme === 'dark'" :size="16" />
+          <Moon v-else :size="16" />
         </button>
 
         <!-- Settings link -->
         <router-link to="/settings" class="btn-icon" aria-label="Settings" title="Settings">
-          <svg width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round">
-            <circle cx="12" cy="12" r="3"/>
-            <path d="M19.4 15a1.65 1.65 0 0 0 .33 1.82l.06.06a2 2 0 0 1-2.83 2.83l-.06-.06a1.65 1.65 0 0 0-1.82-.33 1.65 1.65 0 0 0-1 1.51V21a2 2 0 0 1-4 0v-.09A1.65 1.65 0 0 0 9 19.4a1.65 1.65 0 0 0-1.82.33l-.06.06a2 2 0 0 1-2.83-2.83l.06-.06A1.65 1.65 0 0 0 4.68 15a1.65 1.65 0 0 0-1.51-1H3a2 2 0 0 1 0-4h.09A1.65 1.65 0 0 0 4.6 9a1.65 1.65 0 0 0-.33-1.82l-.06-.06a2 2 0 0 1 2.83-2.83l.06.06A1.65 1.65 0 0 0 9 4.68a1.65 1.65 0 0 0 1-1.51V3a2 2 0 0 1 4 0v.09a1.65 1.65 0 0 0 1 1.51 1.65 1.65 0 0 0 1.82-.33l.06-.06a2 2 0 0 1 2.83 2.83l-.06.06A1.65 1.65 0 0 0 19.4 9a1.65 1.65 0 0 0 1.51 1H21a2 2 0 0 1 0 4h-.09a1.65 1.65 0 0 0-1.51 1z"/>
-          </svg>
+          <Settings :size="16" />
         </router-link>
 
         <div class="user-info">
@@ -137,7 +136,8 @@ router.afterEach(() => {
           <span class="status-text">{{ statusShortLabel }}</span>
         </span>
         <button class="btn-icon" @click="toggleShortcuts">?</button>
-        <button class="btn-icon" @click="toggleTheme">{{ theme === "dark" ? "\u2600" : "\u263E" }}</button>
+        <button class="btn-icon" @click="toggleTheme"><Sun v-if="theme === 'dark'" :size="16" />
+          <Moon v-else :size="16" /></button>
       </div>
       <div class="mobile-user">
         <span class="username">{{ authStore.user?.username }}</span>