Add help modal navigation with table of contents, scroll spy, vault context indicator, and new window button for file viewing

frontend/style.css

@@ -118,10 +118,35 @@ a:hover {
 
 .header-right {
   display: flex;
+  align-items: center;
   justify-content: flex-end;
+  gap: 12px;
   flex: 0 1 auto;
 }
 
+.vault-context-indicator {
+  display: flex;
+  align-items: center;
+  gap: 6px;
+  padding: 6px 12px;
+  background: color-mix(in srgb, var(--accent) 12%, transparent);
+  border: 1px solid color-mix(in srgb, var(--accent) 25%, var(--border));
+  border-radius: 8px;
+  font-family: 'JetBrains Mono', monospace;
+  font-size: 0.75rem;
+  font-weight: 600;
+  color: var(--accent);
+  cursor: default;
+  transition: all 200ms ease;
+}
+.vault-context-indicator:hover {
+  background: color-mix(in srgb, var(--accent) 18%, transparent);
+  border-color: var(--accent);
+}
+.vault-context-indicator i {
+  color: var(--accent);
+}
+
 .hamburger-btn {
   display: none;
   background: none;
@@ -907,9 +932,15 @@ select {
   flex: 1;
   overflow-y: auto;
   padding: clamp(16px, 3vw, 40px) clamp(16px, 4vw, 40px) 60px;
-  transition: background 200ms ease;
+  transition: background 200ms ease, margin 300ms ease;
   min-width: 0;
 }
+
+/* Center content when sidebar is hidden */
+.sidebar.hidden ~ .content-area {
+  margin: 0 auto;
+  max-width: 1200px;
+}
 .content-area::-webkit-scrollbar {
   width: 8px;
 }
@@ -1475,11 +1506,91 @@ select {
 .help-body {
   padding: 0;
   background: radial-gradient(circle at top right, color-mix(in srgb, var(--accent) 10%, transparent), transparent 30%), var(--bg-primary);
+  display: flex;
+  gap: 0;
 }
+
+/* Help Navigation Menu */
+.help-nav {
+  width: 220px;
+  min-width: 220px;
+  background: var(--bg-secondary);
+  border-right: 1px solid var(--border);
+  padding: 20px 0;
+  overflow-y: auto;
+  position: sticky;
+  top: 0;
+  height: calc(90vh - 60px);
+  flex-shrink: 0;
+}
+.help-nav-title {
+  font-family: 'JetBrains Mono', monospace;
+  font-size: 0.75rem;
+  font-weight: 700;
+  text-transform: uppercase;
+  letter-spacing: 0.05em;
+  color: var(--text-muted);
+  padding: 0 20px 12px;
+  border-bottom: 1px solid var(--border);
+  margin-bottom: 8px;
+}
+.help-nav-list {
+  list-style: none;
+  margin: 0;
+  padding: 0;
+}
+.help-nav-list li {
+  margin: 0;
+}
+.help-nav-link {
+  display: block;
+  padding: 8px 20px;
+  font-size: 0.85rem;
+  color: var(--text-secondary);
+  text-decoration: none;
+  transition: all 150ms ease;
+  border-left: 3px solid transparent;
+}
+.help-nav-link:hover {
+  color: var(--accent);
+  background: var(--bg-hover);
+  text-decoration: none;
+}
+.help-nav-link.active {
+  color: var(--accent);
+  background: color-mix(in srgb, var(--accent) 10%, transparent);
+  border-left-color: var(--accent);
+  font-weight: 600;
+}
+
 .help-content {
+  flex: 1;
   max-width: 920px;
   margin: 0 auto;
-  padding: 28px 24px 40px;
+  padding: 28px 32px 40px;
+  overflow-y: auto;
+  min-width: 0;
+}
+.help-lead {
+  font-size: 1.05rem;
+  line-height: 1.6;
+  color: var(--text-primary);
+  margin-bottom: 16px;
+}
+.help-footer {
+  margin-top: 48px;
+  padding-top: 24px;
+  border-top: 1px solid var(--border);
+  text-align: center;
+  color: var(--text-muted);
+  font-size: 0.85rem;
+}
+.help-footer a {
+  color: var(--accent);
+  text-decoration: none;
+}
+.help-footer a:hover {
+  text-decoration: underline;
 }
 .help-content h1,
 .help-content h2,
@@ -1504,6 +1615,17 @@ select {
   margin: 0 0 12px;
   color: var(--text-secondary);
 }
+.help-content ul,
+.help-content ol {
+  margin: 8px 0 16px;
+  padding-left: 24px;
+  color: var(--text-secondary);
+}
+.help-content ul li,
+.help-content ol li {
+  margin: 6px 0;
+  line-height: 1.6;
+}
 .help-content code {
   font-family: 'JetBrains Mono', monospace;
   background: var(--code-bg);
@@ -1511,6 +1633,11 @@ select {
   border-radius: 4px;
   padding: 1px 5px;
   color: var(--text-primary);
+  font-size: 0.88em;
+}
+.help-content strong {
+  color: var(--text-primary);
+  font-weight: 600;
 }
 
 .help-hero {
@@ -1784,6 +1911,19 @@ select {
   word-wrap: break-word;
 }
 
+/* Mobile help navigation */
+@media (max-width: 768px) {
+  .help-nav {
+    display: none;
+  }
+  .help-content {
+    padding: 20px 16px 32px;
+  }
+  .vault-context-indicator {
+    display: none;
+  }
+}
+
 /* Mobile editor */
 @media (max-width: 768px) {
   .editor-modal {