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/Cargo.toml

@@ -8,6 +8,7 @@ dioxus = { workspace = true, features = ["router", "fullstack"] }
 ui = { workspace = true }
 api = { workspace = true }
 uuid = { workspace = true, features = ["js"] }
+markdown = "0.3.0"
 
 [features]
 default = []