feat(auth): implement ticket and API token authentication with session model

Add PveSession, PveAuthenticator, PveVersion, and PveAuthMode. Support
ticket-based auth (username/password with 2hr expiry) and API token auth
(USER@REALM!TOKENID=UUID format). Version detection on connect via
GET /api2/json/version. Custom exception types for API errors, expired
sessions, missing connections, version mismatches, and task failures.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/PSProxmoxVE.Core/Exceptions/PveApiException.cs

@@ -0,0 +1,29 @@
+using System;
+using System.Net;
+
+namespace PSProxmoxVE.Core.Exceptions
+{
+    /// <summary>Exception thrown when the Proxmox VE API returns an error response</summary>
+    public class PveApiException : Exception
+    {
+        public HttpStatusCode StatusCode { get; }
+        public string Resource { get; }
+        public string HttpMethod { get; }
+
+        public PveApiException(HttpStatusCode statusCode, string message, string resource, string httpMethod)
+            : base($"PVE API error ({(int)statusCode} {statusCode}) on {httpMethod} {resource}: {message}")
+        {
+            StatusCode = statusCode;
+            Resource = resource;
+            HttpMethod = httpMethod;
+        }
+
+        public PveApiException(HttpStatusCode statusCode, string message, string resource, string httpMethod, Exception innerException)
+            : base($"PVE API error ({(int)statusCode} {statusCode}) on {httpMethod} {resource}: {message}", innerException)
+        {
+            StatusCode = statusCode;
+            Resource = resource;
+            HttpMethod = httpMethod;
+        }
+    }
+}

src/PSProxmoxVE.Core/Exceptions/PveAuthenticationException.cs

@@ -0,0 +1,18 @@
+using System;
+
+namespace PSProxmoxVE.Core.Exceptions
+{
+    /// <summary>Exception thrown when authentication to a Proxmox VE server fails</summary>
+    public class PveAuthenticationException : Exception
+    {
+        public PveAuthenticationException(string message)
+            : base(message)
+        {
+        }
+
+        public PveAuthenticationException(string message, Exception innerException)
+            : base(message, innerException)
+        {
+        }
+    }
+}

src/PSProxmoxVE.Core/Exceptions/PveNotConnectedException.cs

@@ -0,0 +1,18 @@
+using System;
+
+namespace PSProxmoxVE.Core.Exceptions
+{
+    /// <summary>Exception thrown when an operation is attempted without an active Proxmox VE session</summary>
+    public class PveNotConnectedException : Exception
+    {
+        public PveNotConnectedException()
+            : base("No active Proxmox VE session. Run Connect-PveServer first.")
+        {
+        }
+
+        public PveNotConnectedException(Exception innerException)
+            : base("No active Proxmox VE session. Run Connect-PveServer first.", innerException)
+        {
+        }
+    }
+}

src/PSProxmoxVE.Core/Exceptions/PveSessionExpiredException.cs

@@ -0,0 +1,18 @@
+using System;
+
+namespace PSProxmoxVE.Core.Exceptions
+{
+    /// <summary>Exception thrown when the Proxmox VE session ticket has expired</summary>
+    public class PveSessionExpiredException : Exception
+    {
+        public PveSessionExpiredException()
+            : base("Your Proxmox VE session has expired. Please run Connect-PveServer to establish a new session.")
+        {
+        }
+
+        public PveSessionExpiredException(Exception innerException)
+            : base("Your Proxmox VE session has expired. Please run Connect-PveServer to establish a new session.", innerException)
+        {
+        }
+    }
+}

src/PSProxmoxVE.Core/Exceptions/PveTaskFailedException.cs

@@ -0,0 +1,25 @@
+using System;
+
+namespace PSProxmoxVE.Core.Exceptions
+{
+    /// <summary>Exception thrown when a Proxmox VE task completes with a failed exit status</summary>
+    public class PveTaskFailedException : Exception
+    {
+        public string Upid { get; }
+        public string ExitStatus { get; }
+
+        public PveTaskFailedException(string upid, string exitStatus)
+            : base($"Task {upid} failed with exit status: {exitStatus}")
+        {
+            Upid = upid;
+            ExitStatus = exitStatus;
+        }
+
+        public PveTaskFailedException(string upid, string exitStatus, Exception innerException)
+            : base($"Task {upid} failed with exit status: {exitStatus}", innerException)
+        {
+            Upid = upid;
+            ExitStatus = exitStatus;
+        }
+    }
+}

src/PSProxmoxVE.Core/Exceptions/PveTaskTimeoutException.cs

@@ -0,0 +1,25 @@
+using System;
+
+namespace PSProxmoxVE.Core.Exceptions
+{
+    /// <summary>Exception thrown when a Proxmox VE task does not complete within the allowed timeout period</summary>
+    public class PveTaskTimeoutException : Exception
+    {
+        public string Upid { get; }
+        public TimeSpan Timeout { get; }
+
+        public PveTaskTimeoutException(string upid, TimeSpan timeout)
+            : base($"Task {upid} did not complete within {timeout.TotalSeconds} seconds.")
+        {
+            Upid = upid;
+            Timeout = timeout;
+        }
+
+        public PveTaskTimeoutException(string upid, TimeSpan timeout, Exception innerException)
+            : base($"Task {upid} did not complete within {timeout.TotalSeconds} seconds.", innerException)
+        {
+            Upid = upid;
+            Timeout = timeout;
+        }
+    }
+}

src/PSProxmoxVE.Core/Exceptions/PveVersionException.cs

@@ -0,0 +1,29 @@
+using System;
+using PSProxmoxVE.Core.Authentication;
+
+namespace PSProxmoxVE.Core.Exceptions
+{
+    /// <summary>Exception thrown when the connected Proxmox VE server does not meet the minimum version requirement for an operation</summary>
+    public class PveVersionException : Exception
+    {
+        public int RequiredMajor { get; }
+        public int RequiredMinor { get; }
+        public PveVersion ActualVersion { get; }
+
+        public PveVersionException(int requiredMajor, int requiredMinor, PveVersion actualVersion)
+            : base($"This operation requires Proxmox VE {requiredMajor}.{requiredMinor} or later. Connected server is version {actualVersion}.")
+        {
+            RequiredMajor = requiredMajor;
+            RequiredMinor = requiredMinor;
+            ActualVersion = actualVersion;
+        }
+
+        public PveVersionException(int requiredMajor, int requiredMinor, PveVersion actualVersion, Exception innerException)
+            : base($"This operation requires Proxmox VE {requiredMajor}.{requiredMinor} or later. Connected server is version {actualVersion}.", innerException)
+        {
+            RequiredMajor = requiredMajor;
+            RequiredMinor = requiredMinor;
+            ActualVersion = actualVersion;
+        }
+    }
+}