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
3aa1e90d7f