feat(Greeter): improved multi-user UI and per-user theme sync

- Introduce multi-account greeter login with per-user theme previews
- Add `dms greeter sync --profile` for secondary users with or without sudo
- Add Manage greeter group membership from Settings UI → Users Tab

quickshell/Services/GreeterUsersService.qml

@@ -0,0 +1,163 @@
+pragma Singleton
+
+import QtQuick
+import Quickshell
+import Quickshell.Io
+import qs.Common
+
+Singleton {
+    id: root
+
+    readonly property var log: Log.scoped("GreeterUsersService")
+
+    readonly property string greetCfgDir: Quickshell.env("DMS_GREET_CFG_DIR") || "/var/cache/dms-greeter"
+    readonly property string usersCacheDir: greetCfgDir + "/users"
+
+    property var users: []
+    property var usernames: []
+    property var profileImageMap: ({})
+    property bool loaded: false
+    property bool refreshing: false
+
+    Component.onCompleted: refresh()
+
+    function refresh() {
+        if (refreshing)
+            return;
+        refreshing = true;
+        _loadUsers();
+    }
+
+    function displayName(username) {
+        const u = _findUser(username);
+        if (!u)
+            return username || "";
+        const gecos = (u.gecos || "").trim();
+        return gecos.length > 0 ? gecos : username;
+    }
+
+    function optionLabel(username) {
+        const label = displayName(username);
+        return label !== username ? label : username;
+    }
+
+    function usernameFromOptionLabel(label) {
+        for (let i = 0; i < users.length; i++) {
+            if (root.optionLabel(users[i].username) === label)
+                return users[i].username;
+        }
+        return label;
+    }
+
+    function hasSyncedTheme(username) {
+        if (!username)
+            return false;
+        return syncedThemePaths[username] === true;
+    }
+
+    property var syncedThemePaths: ({})
+
+    function userCacheDir(username) {
+        if (!username)
+            return "";
+        return usersCacheDir + "/" + username;
+    }
+
+    function syncedSettingsPath(username) {
+        const dir = userCacheDir(username);
+        return dir ? dir + "/settings.json" : "";
+    }
+
+    function _findUser(name) {
+        for (let i = 0; i < users.length; i++) {
+            if (users[i].username === name)
+                return users[i];
+        }
+        return null;
+    }
+
+    function _loadUsers() {
+        Proc.runCommand("greeterUsersService-loadUsers", ["sh", "-c", "getent passwd | awk -F: '$3>=1000 && $3<60000 && $1!=\"nobody\" {print $1\":\"$3\":\"$5\":\"$6\":\"$7}'"], (output, exitCode) => {
+            const lines = (output || "").trim().split("\n").filter(l => l.length > 0);
+            const list = [];
+            const names = [];
+            for (let i = 0; i < lines.length; i++) {
+                const parts = lines[i].split(":");
+                if (parts.length < 5)
+                    continue;
+                const username = parts[0];
+                list.push({
+                    username,
+                    uid: parseInt(parts[1], 10),
+                    gecos: (parts[2] || "").split(",")[0],
+                    home: parts[3] || "",
+                    shell: parts[4] || ""
+                });
+                names.push(username);
+            }
+            list.sort((a, b) => a.username.localeCompare(b.username));
+            names.sort((a, b) => a.localeCompare(b));
+            root.users = list;
+            root.usernames = names;
+            root.loaded = true;
+            root.refreshing = false;
+            _refreshSyncedThemeFlags();
+            _loadProfileIcons();
+        }, 0);
+    }
+
+    function _refreshSyncedThemeFlags() {
+        if (usernames.length === 0) {
+            syncedThemePaths = ({});
+            return;
+        }
+        const checks = usernames.map(u => `[ -f "${syncedSettingsPath(u)}" ] && echo "${u}:1" || echo "${u}:0"`).join("; ");
+        Proc.runCommand("greeterUsersService-syncedThemes", ["sh", "-c", checks], (output, exitCode) => {
+            const map = {};
+            const lines = (output || "").trim().split("\n").filter(l => l.length > 0);
+            for (let i = 0; i < lines.length; i++) {
+                const parts = lines[i].split(":");
+                if (parts.length >= 2)
+                    map[parts[0]] = parts[1] === "1";
+            }
+            root.syncedThemePaths = map;
+        }, 0);
+    }
+
+    function profileImagePath(username) {
+        if (!username)
+            return "";
+        return profileImageMap[username] || "";
+    }
+
+    function _loadProfileIcons() {
+        if (users.length === 0) {
+            profileImageMap = ({});
+            return;
+        }
+        const script = users.map(u => {
+            const safeUser = u.username.replace(/'/g, "'\\''");
+            const safeHome = (u.home || "").replace(/'/g, "'\\''");
+            const cacheDir = usersCacheDir + "/" + u.username;
+            return `( icon=""; for f in "${cacheDir}/profile.jpg" "${cacheDir}/profile.jpeg" "${cacheDir}/profile.png" "${cacheDir}/profile.webp" "/var/lib/AccountsService/icons/${safeUser}" "${safeHome}/.face" "${safeHome}/.face.icon"; do if [ -f "$f" ] && [ -r "$f" ]; then icon="$f"; break; fi; done; echo "${u.username}:$icon" )`;
+        }).join("; ");
+        Proc.runCommand("greeterUsersService-profileIcons", ["sh", "-c", script], (output, exitCode) => {
+            const map = {};
+            const lines = (output || "").trim().split("\n").filter(l => l.length > 0);
+            for (let i = 0; i < lines.length; i++) {
+                const idx = lines[i].indexOf(":");
+                if (idx <= 0)
+                    continue;
+                const user = lines[i].substring(0, idx);
+                const icon = lines[i].substring(idx + 1).trim();
+                map[user] = icon && icon.length > 0 ? icon : "";
+            }
+            for (let j = 0; j < users.length; j++) {
+                const u = users[j].username;
+                if (!(u in map))
+                    map[u] = "";
+            }
+            root.profileImageMap = map;
+        }, 0);
+    }
+}