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>

core/src/sync/sharing.rs

@@ -8,7 +8,7 @@
 
 use rusqlite::params;
 
-use super::client::{self, Member, NoteShare};
+use super::client::{self, Directory, NoteShare, ShareTarget};
 use super::state;
 use crate::local::Db;
 
@@ -38,7 +38,7 @@ fn mark_shared(db: &Db, note_id: &str, shares: &[NoteShare]) -> Result<(), Strin
     Ok(())
 }
 
-pub async fn directory(db: &Db) -> Result<Vec<Member>, String> {
+pub async fn directory(db: &Db) -> Result<Directory, String> {
     let (url, token) = link(db)?;
     client::directory(&url, &token).await
 }
@@ -53,11 +53,11 @@ pub async fn list(db: &Db, note_id: &str) -> Result<Vec<NoteShare>, String> {
 pub async fn share(
     db: &Db,
     note_id: &str,
-    user_id: &str,
+    target: &ShareTarget,
     permission: &str,
 ) -> Result<Vec<NoteShare>, String> {
     let (url, token) = link(db)?;
-    let shares = client::share_note(&url, &token, note_id, user_id, permission).await?;
+    let shares = client::share_note(&url, &token, note_id, target, permission).await?;
     mark_shared(db, note_id, &shares)?;
     Ok(shares)
 }
@@ -73,6 +73,7 @@ pub async fn unshare(db: &Db, note_id: &str, share_id: &str) -> Result<Vec<NoteS
 mod tests {
     use super::*;
     use crate::local::schema;
+    use crate::sync::client::Member;
     use rusqlite::Connection;
     use std::sync::Mutex;
 
@@ -101,11 +102,12 @@ mod tests {
         }
         let one = NoteShare {
             id: "s1".into(),
-            member: Member {
+            member: Some(Member {
                 id: "u2".into(),
                 display_name: "Sam".into(),
                 email: "sam@example.test".into(),
-            },
+            }),
+            group: None,
             permission: "view".into(),
             created_at: None,
         };