feat(design): surface phase PR 5 — Project + Workspace polish

Per the surface-phase spec for the Project list, Project view, and
3-panel Workspace cluster:

Button reclassification per Hybrid rule
- ProjectView:
  - btn-workspace ("Open Workspace"): kept on accent gradient — the
    workspace is the project's central feature moment, a Scribe-
    flavored action, brand moment per the doc.
  - btn-share: muted-outline → Bronze action-secondary
  - btn-danger-outline (Delete project): generic-border + danger-on-
    hover → Oxblood outline + filled hover (proper destructive)
  - btn-save-panel: accent gradient → Moss action-primary
  - btn-ms-confirm (milestone confirm): flat accent → Moss
  - btn-ms-cancel: ghost → Bronze action-secondary
  - .modal-btn-danger: --color-danger → --color-action-destructive
- ProjectListView:
  - btn-primary ("+ New Project"): flat accent → Moss action-primary.
    Empty-state CTA (.empty-action) keeps accent — that *is* a
    brand moment per Hybrid, "create your first project".
- WorkspaceTaskPanel + WorkspaceNoteEditor:
  - btn-delete-task / btn-delete: hover --color-danger → Oxblood
  - btn-delete-confirm / btn-confirm-delete: --color-danger pair →
    --color-action-destructive pair, with filled hover for stronger
    affordance
  - btn-save (WorkspaceNoteEditor): flat accent → Moss
- WorkspaceChatWidget:
  - History toggle: replaced unicode ▾ with Lucide ChevronDown
    (PR 1 carry-over for emoji-as-icon)

Two-weights-only
- Snapped every font-weight 600/700 to 500 across the cluster.

Borders kept (per structural-not-decorative rule)
- Milestone group cards: standalone containers, keep
- Project cards in list: standalone containers, keep
- Task slide-over panel: drawer modal, keep
- Workspace 3-panel separators: major section dividers, keep

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

frontend/src/components/WorkspaceChatWidget.vue

@@ -180,7 +180,9 @@ defineExpose({ prefill });
             :class="{ active: historyOpen }"
             title="History"
             @click="toggleHistory"
-          >▾</button>
+          >
+            <ChevronDown :size="16" />
+          </button>
           <div v-if="historyOpen" class="ws-chat-history-menu">
             <div v-if="projectConversations.length === 0" class="ws-chat-history-empty">
               No past conversations
@@ -263,7 +265,7 @@ defineExpose({ prefill });
 }
 .ws-chat-title {
   font-size: 0.78rem;
-  font-weight: 600;
+  font-weight: 500;
   text-transform: uppercase;
   letter-spacing: 0.06em;
   color: var(--color-text-muted);
@@ -338,7 +340,7 @@ defineExpose({ prefill });
 }
 .ws-chat-history-item.current {
   color: var(--color-primary);
-  font-weight: 600;
+  font-weight: 500;
 }
 .ws-chat-history-title {
   display: block;