feat: add favorites section with star button, frontmatter persistence, and drag-to-reorder

Adds FAVORITES sidebar section backed by _favorite and _favorite_index
frontmatter properties. Star button in breadcrumb bar toggles favorite
state. Drag-to-reorder updates _favorite_index on all affected notes.
Section auto-hides when empty.

ADR 0038 documents the decision to use frontmatter for portability.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src-tauri/src/vault/entry.rs

@@ -59,6 +59,11 @@ pub struct VaultEntry {
     pub view: Option<String>,
     /// Whether this Type is visible in the sidebar. Defaults to true when absent.
     pub visible: Option<bool>,
+    /// Whether this note is a user favorite (shown in FAVORITES sidebar section).
+    pub favorite: bool,
+    /// Display order within the FAVORITES section (lower = higher).
+    #[serde(rename = "favoriteIndex")]
+    pub favorite_index: Option<i64>,
     /// Word count of the note body (excludes frontmatter and H1 title).
     #[serde(rename = "wordCount")]
     pub word_count: u32,

src-tauri/src/vault/frontmatter.rs

@@ -45,6 +45,14 @@ pub(crate) struct Frontmatter {
     pub view: Option<StringOrList>,
     #[serde(default)]
     pub visible: Option<bool>,
+    #[serde(
+        rename = "_favorite",
+        default,
+        deserialize_with = "deserialize_bool_or_string"
+    )]
+    pub favorite: Option<bool>,
+    #[serde(rename = "_favorite_index", default)]
+    pub favorite_index: Option<i64>,
 }
 
 /// Custom deserializer for boolean fields that may arrive as strings.
@@ -154,6 +162,8 @@ fn parse_frontmatter(data: &HashMap<String, serde_json::Value>) -> Frontmatter {
         "notion_id",
         "Status",
         "status",
+        "_favorite",
+        "_favorite_index",
     ];
     let filtered: serde_json::Map<String, serde_json::Value> = data
         .iter()
@@ -184,6 +194,8 @@ const SKIP_KEYS: &[&str] = &[
     "view",
     "visible",
     "status",
+    "_favorite",
+    "_favorite_index",
 ];
 
 /// Extract all wikilink-containing fields from raw YAML frontmatter.

src-tauri/src/vault/mod.rs

@@ -102,6 +102,8 @@ pub fn parse_md_file(path: &Path) -> Result<VaultEntry, String> {
         sort: frontmatter.sort.and_then(|v| v.into_scalar()),
         view: frontmatter.view.and_then(|v| v.into_scalar()),
         visible: frontmatter.visible,
+        favorite: frontmatter.favorite.unwrap_or(false),
+        favorite_index: frontmatter.favorite_index,
         word_count,
         outgoing_links,
         properties,