feat: add filter bar markup and pill button styles to trip page

Replace the old trip-nav links with a new filter bar component featuring:
- Three pill buttons for filtering (All content, Journal, Stories)
- "All content" button active by default with teal accent styling
- Separate Stats button with matching pill styling
- CSS for buttons with hover and active states
- Responsive flexbox layout that wraps on narrow screens

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RB86BaJBG3eGiMdfhmHRrQ

themes/intotheeast/css/style.css

@@ -693,6 +693,50 @@ body::after {
     color: var(--color-ink-muted);
 }
 
+/* ── Trip page filter bar ────────────────────────────────────────────────────── */
+
+.trip-filter-bar {
+    display: flex;
+    align-items: center;
+    justify-content: space-between;
+    gap: var(--space-3);
+    margin-top: var(--space-4);
+    flex-wrap: wrap;
+}
+
+.trip-filter-group {
+    display: flex;
+    gap: var(--space-2);
+    flex-wrap: wrap;
+}
+
+.trip-filter-btn,
+.trip-stats-btn {
+    font-family: var(--font-ui);
+    font-size: var(--text-sm);
+    font-weight: 500;
+    color: var(--color-ink-muted);
+    background: transparent;
+    border: 1px solid var(--color-border);
+    border-radius: var(--radius-full);
+    padding: var(--space-1) var(--space-4);
+    cursor: pointer;
+    transition: color 0.15s, border-color 0.15s, background 0.15s;
+}
+
+.trip-filter-btn:hover,
+.trip-stats-btn:hover {
+    color: var(--color-ink);
+    border-color: var(--color-ink-muted);
+}
+
+.trip-filter-btn.is-active,
+.trip-stats-btn.is-active {
+    color: var(--color-accent);
+    border-color: var(--color-accent);
+    background: var(--color-accent-light);
+}
+
 @media (max-width: 768px) {
     .home-layout { display: flex; flex-direction: column; }
     .home-map-col { position: static; height: 40vh; align-self: stretch; }