feat: Add per-user IP limit exemption

Introduces a new 'unlimited_user' flag for users. When set to true, the user is exempt from the concurrent IP limit enforcement by `limit.sh`.

- `core/scripts/hysteria2/add_user.py`:
  - Adds an optional `unlimited_user` argument (defaults to false).
  - Stores the `unlimited_user` boolean in the `users.json` file when adding a user.

- `core/scripts/hysteria2/limit.sh`:
  - Modifies `check_ip_limit` function to first check the `unlimited_user` flag for the connecting user in `users.json`.
  - If the flag is true, the script bypasses the IP limit check for that user.
  - Uses `jq` for reliable parsing and includes a `grep` fallback for systems without `jq`.
  - Existing users without the flag are treated as limited (default behavior).

core/scripts/hysteria2/limit.sh

@@ -183,6 +183,23 @@ check_ip_limit() {
     local username="$1"
     local ips=()
 
+    local is_unlimited="false"
+    if [ -f "$USERS_FILE" ]; then
+        if command -v jq &>/dev/null; then
+            is_unlimited=$(jq -r --arg user "$username" '.[$user].unlimited_user // "false"' "$USERS_FILE" 2>/dev/null)
+        else
+            if grep -q "\"$username\"" "$USERS_FILE" && \
+               grep -A 5 "\"$username\"" "$USERS_FILE" | grep -q '"unlimited_user": true'; then
+                is_unlimited="true"
+            fi
+        fi
+    fi
+
+    if [ "$is_unlimited" = "true" ]; then
+        log_message "INFO" "User $username is exempt from IP limit. Skipping check."
+        return
+    fi
+
     # Get all IPs for this user
     if command -v jq &>/dev/null; then
         readarray -t ips < <(jq -r --arg user "$username" '.[$user][]' "$CONNECTIONS_FILE" 2>/dev/null)
@@ -364,4 +381,4 @@ case "$1" in
         ;;
 esac
 
-exit 0
+exit 0