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

Cargo.lock

@@ -2907,6 +2907,17 @@ dependencies = [
  "syn 2.0.114",
 ]
 
+[[package]]
+name = "markdown"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ef3aab6a1d529b112695f72beec5ee80e729cb45af58663ec902c8fac764ecdd"
+dependencies = [
+ "lazy_static",
+ "pipeline",
+ "regex",
+]
+
 [[package]]
 name = "markup5ever"
 version = "0.14.1"
@@ -3542,6 +3553,12 @@ version = "0.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8b870d8c151b6f2fb93e84a13146138f05d02ed11c7e7c54f8826aaaf7c9f184"
 
+[[package]]
+name = "pipeline"
+version = "0.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d15b6607fa632996eb8a17c9041cb6071cb75ac057abd45dece578723ea8c7c0"
+
 [[package]]
 name = "pkg-config"
 version = "0.3.32"
@@ -3905,6 +3922,18 @@ dependencies = [
  "thiserror 2.0.18",
 ]
 
+[[package]]
+name = "regex"
+version = "1.12.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e10754a14b9137dd7b1e3e5b0493cc9171fdd105e0ab477f51b72e7f3ac0e276"
+dependencies = [
+ "aho-corasick",
+ "memchr",
+ "regex-automata",
+ "regex-syntax",
+]
+
 [[package]]
 name = "regex-automata"
 version = "0.4.14"
@@ -5366,6 +5395,7 @@ version = "0.1.0"
 dependencies = [
  "api",
  "dioxus",
+ "markdown",
  "ui",
  "uuid",
 ]