web, core, desktop: share a note with a group, and Settings → Groups

The Share dialog lists people and groups in one picker and shows a group share
as its name and member count. Settings gains a Groups section for the admin:
create, rename, delete, and add or remove people.

The core client reads the directory's groups and group shares (ShareTarget:
a member or a group); the desktop command takes user_id or group_id.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

desktop/src-tauri/src/commands/sync.rs

@@ -8,7 +8,7 @@ use tauri::{AppHandle, State};
 
 use inkwell_core::local::Db;
 use inkwell_core::sync::client::{self, Identity, ProbeResult};
-use inkwell_core::sync::client::{Member, NoteShare};
+use inkwell_core::sync::client::{Directory, NoteShare, ShareTarget};
 use inkwell_core::sync::compat::Compatibility;
 use inkwell_core::sync::engine;
 use inkwell_core::sync::push;
@@ -193,7 +193,7 @@ pub fn sync_has_pending(db: State<'_, Db>) -> Result<bool, String> {
 // `sharing::NEEDS_SERVER`, which the dialog shows as it is.
 
 #[tauri::command]
-pub async fn shares_directory(db: State<'_, Db>) -> Result<Vec<Member>, String> {
+pub async fn shares_directory(db: State<'_, Db>) -> Result<Directory, String> {
     sharing::directory(&db).await
 }
 
@@ -202,14 +202,21 @@ pub async fn shares_list(note_id: String, db: State<'_, Db>) -> Result<Vec<NoteS
     sharing::list(&db, &note_id).await
 }
 
+/// Share with a person (`user_id`) or a group (`group_id`, #5177): exactly one.
 #[tauri::command]
 pub async fn shares_share(
     note_id: String,
-    user_id: String,
+    user_id: Option<String>,
+    group_id: Option<String>,
     permission: String,
     db: State<'_, Db>,
 ) -> Result<Vec<NoteShare>, String> {
-    sharing::share(&db, &note_id, &user_id, &permission).await
+    let target = match (user_id, group_id) {
+        (Some(id), None) => ShareTarget::Member(id),
+        (None, Some(id)) => ShareTarget::Group(id),
+        _ => return Err("Choose someone or a group to share with.".to_string()),
+    };
+    sharing::share(&db, &note_id, &target, &permission).await
 }
 
 #[tauri::command]