feat(design): surface phase PR 3 — Chat surface polish

Per the surface-phase spec for the Chat cluster (ChatView, ChatPanel,
ChatMessage, ChatInputBar, ToolCallCard):

Long-form line-height
- ChatMessage: assistant-bubble .message-content jumps from 1.55 to
  1.7 — chat is a reading surface, not a snippet stream. User
  bubbles stay tighter.
- JournalView: dropped its :deep(.role-assistant .message-content)
  override; ChatMessage handles it now and Journal inherits.

ToolCallCard borders
- Removed the outer 1px border. ToolCallCard always renders inside
  an assistant bubble; the bubble already contains it. Background
  tint differentiates without re-bordering. Per the
  structural-not-decorative rule.
- Error state preserved as a 3px left-edge accent in --color-danger,
  mirroring the assistant bubble's own left-edge pattern.

Button reclassification per Hybrid rule
- ChatView .bulk-link "All"/"None": accent text → --color-text-secondary
  (these are tertiary list-control affordances, not brand moments)
- ChatView .bulk-delete-btn: --color-danger (Error terracotta) →
  --color-action-destructive (Oxblood) per Hybrid; paired with a
  Trash2 icon since destructive should always be reinforced by an
  icon, not just color
- ChatView .btn-delete-conv hover: same Error → Oxblood swap
- .btn-new-conv stays accent (brand moment, correct already)
- .btn-send stays accent gradient (primary brand moment, foundation)

Two-weights-only
- Snapped every font-weight: 600/700 to 500 across ChatView,
  ChatPanel, ChatMessage, ToolCallCard per the doc rule.

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

frontend/src/views/JournalView.vue

@@ -389,12 +389,6 @@ onMounted(async () => {
 
 .journal-chat-panel { flex: 1; min-height: 0; }
 
-/* Long-form reading line-height for journal assistant bubbles
-   (the daily prep is prose, not chat snippets — wants the doc's 1.7) */
-.journal-chat-panel :deep(.role-assistant .message-content) {
-  line-height: 1.7;
-}
-
 /* ── Right column ─────────────────────────────────────────────────────────── */
 .journal-right {
   grid-column: 2;