feat: add vikunja doctor command for diagnostic checks (#2165)

Add a new `vikunja doctor` CLI command that performs diagnostic checks.

Checks performed:

- **System**: Version, Go version, OS/arch, running user, working
directory
- **Configuration**: Config file path, public URL, JWT secret, CORS
origins
- **Database**: Connection test, server version
(SQLite/MySQL/PostgreSQL)
- **Files**: Storage path, writability, disk space (Unix only)
- **Optional services** (when enabled):
  - Redis: Connection ping
  - Typesense: Health endpoint
  - Mailer: SMTP connection
  - LDAP: Bind authentication test
  - OpenID Connect: Discovery endpoint for each configured provider

pkg/cmd/doctor.go

@@ -0,0 +1,68 @@
+// Vikunja is a to-do list application to facilitate your life.
+// Copyright 2018-present Vikunja and contributors. All rights reserved.
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+package cmd
+
+import (
+	"fmt"
+	"os"
+
+	"code.vikunja.io/api/pkg/config"
+	"code.vikunja.io/api/pkg/doctor"
+	"code.vikunja.io/api/pkg/log"
+
+	"github.com/spf13/cobra"
+)
+
+func init() {
+	rootCmd.AddCommand(doctorCmd)
+}
+
+var doctorCmd = &cobra.Command{
+	Use:   "doctor",
+	Short: "Run diagnostic checks on your Vikunja installation",
+	Long: `The doctor command runs a series of diagnostic checks to help troubleshoot
+issues with your Vikunja installation. It checks:
+
+- System information (version, user, working directory)
+- Configuration (config file, public URL, JWT secret, CORS)
+- Database connectivity and version
+- File storage (local or S3)
+- Optional services (Redis, Typesense, Mailer, LDAP, OpenID)
+
+Exit codes:
+  0 - All checks passed
+  1 - One or more checks failed`,
+	PreRun: func(_ *cobra.Command, _ []string) {
+		// Minimal init - just config and logger
+		// Each check will initialize and test its own components
+		log.InitLogger()
+		config.InitConfig()
+	},
+	Run: func(_ *cobra.Command, _ []string) {
+		results := doctor.Run()
+
+		doctor.PrintResults(os.Stdout, results)
+
+		failed := doctor.CountFailed(results)
+		if failed > 0 {
+			fmt.Printf("%d check(s) failed\n", failed)
+			os.Exit(1)
+		}
+
+		fmt.Println("All checks passed")
+	},
+}