feat: add auto-save debounce, note refetch on switch, todos feature with markdown

Features implemented:
- Auto-save with counter-based debounce in note editor
- Note refetches when switching between notes (note_id prop changes)
- Todos feature with full CRUD operations
- Markdown rendering in todo titles
- API endpoints for todos (create, list, toggle, delete)
- Todo panel in sidebar with sorting (incomplete first, newest first)
- Todo items use TodoItem component for clean separation

Technical changes:
- Added Todo struct and API endpoints in api package
- Added markdown dependency to web package
- Implemented TodoPanel component with TodoItem sub-component
- Added mut keywords to signal bindings for Dioxus 0.7
- Fixed closure capture issues with cloning todo objects

packages/web/assets/braindump.css

@@ -449,6 +449,161 @@ body {
     background: var(--text-muted);
 }
 
+.todos-section {
+    padding: 1rem 1.5rem 0.5rem;
+    border-bottom: 1px solid var(--border);
+    background: var(--bg-tertiary);
+}
+
+.todos-title {
+    font-size: 1rem;
+    font-weight: 600;
+    margin-bottom: 1rem;
+    color: var(--text-primary);
+    display: flex;
+    align-items: center;
+    gap: 0.5rem;
+}
+
+.todos-title::before {
+    content: "📋";
+    font-size: 1.2rem;
+}
+
+.todo-form {
+    display: flex;
+    gap: 0.5rem;
+    margin-bottom: 1rem;
+}
+
+.todo-input {
+    flex: 1;
+    padding: 0.6rem 0.8rem;
+    border: 1px solid var(--border);
+    border-radius: 6px;
+    background: var(--bg-primary);
+    color: var(--text-primary);
+    font-size: 0.85rem;
+    outline: none;
+    transition: all 0.2s;
+}
+
+.todo-input:focus {
+    border-color: var(--accent);
+    box-shadow: 0 0 0 3px rgba(139, 92, 246, 0.2);
+}
+
+.todo-input::placeholder {
+    color: var(--text-muted);
+}
+
+.todo-add-button {
+    padding: 0.6rem 1rem;
+    background: var(--accent);
+    color: white;
+    border: none;
+    border-radius: 6px;
+    font-size: 0.85rem;
+    font-weight: 600;
+    cursor: pointer;
+    transition: all 0.2s;
+}
+
+.todo-add-button:hover {
+    background: var(--accent-hover);
+}
+
+.todos-list {
+    display: flex;
+    flex-direction: column;
+    gap: 0.5rem;
+}
+
+.todo-item {
+    display: flex;
+    align-items: center;
+    gap: 0.75rem;
+    padding: 0.75rem 0.8rem;
+    background: var(--bg-secondary);
+    border: 1px solid var(--border);
+    border-radius: 6px;
+    transition: all 0.2s;
+    cursor: pointer;
+}
+
+.todo-item:hover {
+    border-color: var(--accent);
+    background: var(--bg-hover);
+}
+
+.todo-item.completed {
+    opacity: 0.6;
+}
+
+.todo-item.completed .todo-title {
+    text-decoration: line-through;
+    color: var(--text-muted);
+}
+
+.todo-checkbox {
+    width: 18px;
+    height: 18px;
+    cursor: pointer;
+    accent-color: var(--accent);
+}
+
+.todo-title {
+    flex: 1;
+    font-size: 0.9rem;
+    color: var(--text-primary);
+    line-height: 1.4;
+}
+
+.todo-title strong {
+    font-weight: 700;
+}
+
+.todo-title em {
+    font-style: italic;
+}
+
+.todo-title code {
+    background: var(--bg-tertiary);
+    padding: 0.2rem 0.4rem;
+    border-radius: 4px;
+    font-family: 'Consolas', 'Monaco', monospace;
+    font-size: 0.85rem;
+}
+
+.todo-title a {
+    color: var(--accent);
+    text-decoration: none;
+}
+
+.todo-title a:hover {
+    text-decoration: underline;
+}
+
+.todo-delete-button {
+    width: 24px;
+    height: 24px;
+    background: transparent;
+    border: none;
+    color: var(--text-muted);
+    cursor: pointer;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    border-radius: 4px;
+    transition: all 0.2s;
+    font-size: 1rem;
+}
+
+.todo-delete-button:hover {
+    background: var(--danger);
+    color: white;
+}
+
 @media (max-width: 768px) {
     .sidebar {
         width: 100%;