Add admin user management with is_active enforcement

Admin users page at /admin/users with paginated user list showing name,
email, team counts, role, join date, and active status toggle. Inactive
users are blocked from all authenticated endpoints immediately via DB
check in JWT middleware. OAuth login errors now show human-readable
messages on the login page.

internal/api/handlers_users.go

@@ -1,22 +1,27 @@
 package api
 
 import (
+	"fmt"
 	"net/http"
 	"strings"
+	"time"
 
+	"github.com/go-chi/chi/v5"
 	"github.com/jackc/pgx/v5/pgtype"
 
 	"git.omukk.dev/wrenn/wrenn/internal/auth"
 	"git.omukk.dev/wrenn/wrenn/internal/db"
 	"git.omukk.dev/wrenn/wrenn/internal/id"
+	"git.omukk.dev/wrenn/wrenn/internal/service"
 )
 
 type usersHandler struct {
-	db *db.Queries
+	db  *db.Queries
+	svc *service.UserService
 }
 
-func newUsersHandler(db *db.Queries) *usersHandler {
-	return &usersHandler{db: db}
+func newUsersHandler(db *db.Queries, svc *service.UserService) *usersHandler {
+	return &usersHandler{db: db, svc: svc}
 }
 
 // Search handles GET /v1/users/search?email=<prefix>
@@ -50,3 +55,91 @@ func (h *usersHandler) Search(w http.ResponseWriter, r *http.Request) {
 	}
 	writeJSON(w, http.StatusOK, resp)
 }
+
+// AdminListUsers handles GET /v1/admin/users?page=1
+// Returns a paginated list of all users with team counts.
+func (h *usersHandler) AdminListUsers(w http.ResponseWriter, r *http.Request) {
+	page := 1
+	if p := r.URL.Query().Get("page"); p != "" {
+		if _, err := fmt.Sscanf(p, "%d", &page); err != nil || page < 1 {
+			page = 1
+		}
+	}
+	const perPage = 100
+	offset := int32((page - 1) * perPage)
+
+	users, total, err := h.svc.AdminListUsers(r.Context(), perPage, offset)
+	if err != nil {
+		status, code, msg := serviceErrToHTTP(err)
+		writeError(w, status, code, msg)
+		return
+	}
+
+	type adminUserResponse struct {
+		ID          string `json:"id"`
+		Email       string `json:"email"`
+		Name        string `json:"name"`
+		IsAdmin     bool   `json:"is_admin"`
+		IsActive    bool   `json:"is_active"`
+		CreatedAt   string `json:"created_at"`
+		TeamsJoined int32  `json:"teams_joined"`
+		TeamsOwned  int32  `json:"teams_owned"`
+	}
+
+	resp := make([]adminUserResponse, len(users))
+	for i, u := range users {
+		resp[i] = adminUserResponse{
+			ID:          id.FormatUserID(u.ID),
+			Email:       u.Email,
+			Name:        u.Name,
+			IsAdmin:     u.IsAdmin,
+			IsActive:    u.IsActive,
+			CreatedAt:   u.CreatedAt.Format(time.RFC3339),
+			TeamsJoined: u.TeamsJoined,
+			TeamsOwned:  u.TeamsOwned,
+		}
+	}
+
+	totalPages := (total + perPage - 1) / perPage
+	writeJSON(w, http.StatusOK, map[string]any{
+		"users":       resp,
+		"total":       total,
+		"page":        page,
+		"per_page":    perPage,
+		"total_pages": totalPages,
+	})
+}
+
+// SetUserActive handles PUT /v1/admin/users/{id}/active
+// Enables or disables a user account. Admins cannot deactivate themselves.
+func (h *usersHandler) SetUserActive(w http.ResponseWriter, r *http.Request) {
+	ac := auth.MustFromContext(r.Context())
+	userIDStr := chi.URLParam(r, "id")
+
+	userID, err := id.ParseUserID(userIDStr)
+	if err != nil {
+		writeError(w, http.StatusBadRequest, "invalid_request", "invalid user ID")
+		return
+	}
+
+	var req struct {
+		Active bool `json:"active"`
+	}
+	if err := decodeJSON(r, &req); err != nil {
+		writeError(w, http.StatusBadRequest, "invalid_request", "invalid JSON body")
+		return
+	}
+
+	if ac.UserID == userID && !req.Active {
+		writeError(w, http.StatusBadRequest, "invalid_request", "cannot deactivate your own account")
+		return
+	}
+
+	if err := h.svc.SetUserActive(r.Context(), userID, req.Active); err != nil {
+		status, code, msg := serviceErrToHTTP(err)
+		writeError(w, status, code, msg)
+		return
+	}
+
+	w.WriteHeader(http.StatusNoContent)
+}