Move users, calendars, and address books from config.yaml into the database

BREAKING CHANGE: the users:/config-based collection setup is gone. All
user, calendar, and address-book data now lives in the SQLite DB
(internal/db) and is managed exclusively via nidusctl or the web UI.
Existing deployments must recreate their users after upgrading:
  nidusctl user create <username>
  nidusctl calendar create <username> <name>
  nidusctl addressbook create <username> <name>

- internal/db: new users, calendars, addressbooks tables with FK cascade
  delete; foreign_keys pragma enabled; internal/db/users.go implements
  full CRUD + bcrypt auth (CreateUser, VerifyPassword, ListUsers,
  CreateCalendar/AddressBook, etc).
- internal/config: removed Users/UserConfig entirely.
- internal/auth: Basic Auth now checks credentials via db.DB instead of
  cfg.Users.
- internal/caldav, internal/carddav: ListCalendars/ListAddressBooks and
  Create/Delete now backed by the DB.
- internal/web: login uses db.VerifyPassword; new resources.go adds
  create/delete handlers for calendars/address books at
  /web/resources/{calendar,addressbook}; dashboard gained create forms
  and per-card delete buttons (templ + htmx, no hyperscript).
- tools/nidusctl: new user create/delete/list/passwd commands (masked
  interactive password prompt via golang.org/x/term) plus create/delete/
  list subcommands for calendar/addressbook.
- cmd/server/main.go: pre-creates on-disk collections from the DB at
  startup instead of cfg.Users; warns when no users exist yet.
- Updated tests to seed data via the DB; added resources_test.go for the
  new web UI handlers.
- README.md and .github/copilot-instructions.md updated to document the
  new nidusctl commands and the DB-backed architecture.

Verified end-to-end against a live test server: nidusctl user/calendar/
addressbook create, DAV Basic Auth PROPFIND, web login, dashboard
rendering, and web UI create/delete of resources all confirmed working.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

internal/web/server.go

@@ -13,7 +13,6 @@ import (
 	"github.com/yourusername/caldav-server/internal/config"
 	"github.com/yourusername/caldav-server/internal/db"
 	"github.com/yourusername/caldav-server/internal/store"
-	"golang.org/x/crypto/bcrypt"
 )
 
 // Server holds the dependencies needed by the web UI handlers.
@@ -43,19 +42,16 @@ func (s *Server) Handler(staticFS http.FileSystem) http.Handler {
 	mux.HandleFunc("/", s.requireLogin(s.handleDashboard))
 	mux.HandleFunc("/shares/calendar", s.requireLogin(s.handleCalendarShare))
 	mux.HandleFunc("/shares/addressbook", s.requireLogin(s.handleAddressBookShare))
+	mux.HandleFunc("/resources/calendar", s.requireLogin(s.handleCalendarResource))
+	mux.HandleFunc("/resources/addressbook", s.requireLogin(s.handleAddressBookResource))
 
 	return mux
 }
 
-// authenticate validates username/password against the configured users,
-// mirroring internal/auth's Basic Auth check.
+// authenticate validates username/password against the database, mirroring
+// internal/auth's Basic Auth check.
 func (s *Server) authenticate(username, password string) bool {
-	user, ok := s.cfg.Users[username]
-	if !ok {
-		_ = bcrypt.CompareHashAndPassword([]byte("$2b$12$invalidinvalidinvalidinvalidinvalidinval"), []byte(password))
-		return false
-	}
-	return bcrypt.CompareHashAndPassword([]byte(user.Password), []byte(password)) == nil
+	return s.dbase.VerifyPassword(username, password)
 }
 
 func (s *Server) handleLogin(w http.ResponseWriter, r *http.Request) {