refactor: remove legacy patterns system, unify on workflows

Remove the entire patterns domain model, IPC channels, sidecar services,
renderer components, and tests. Sessions now bind exclusively to workflows
via workflowId. Builtin workflows replace builtin patterns.

Backend:
- Make AgentNodeConfig standalone (no longer extends PatternAgentDefinition)
- Add WorkflowOrchestrationMode and WorkflowExecutionDefinition
- Create builtin workflows (single-agent, sequential, concurrent, handoff, group-chat)
- Rewrite session model config helpers for workflow-only
- Remove pattern IPC channels, handlers, and preload bindings
- Merge createSession/createWorkflowSession into single method
- Remove sidecar PatternGraphResolver, PatternValidator, pattern DTOs
- Add workspace migration for legacy sessions (patternId -> workflowId)

Frontend:
- Delete PatternEditor, pattern-graph components, patternGraph lib
- Delete NewSessionModal (session creation uses workflows directly)
- Remove PatternsSection from SettingsPanel
- Update App.tsx, ChatPane, ActivityPanel, Sidebar, RunTimeline,
  AgentConfigFields, InlinePills, sessionActivity to use workflow types
- Delete pattern.ts domain module

78 files changed across backend and frontend.

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

sidecar/src/Aryx.AgentHost/Services/SidecarProtocolHost.cs

@@ -10,7 +10,6 @@ namespace Aryx.AgentHost.Services;
 public sealed class SidecarProtocolHost
 {
     private const string DescribeCapabilitiesCommandType = "describe-capabilities";
-    private const string ValidatePatternCommandType = "validate-pattern";
     private const string ValidateWorkflowCommandType = "validate-workflow";
     private const string RunTurnCommandType = "run-turn";
     private const string CancelTurnCommandType = "cancel-turn";
@@ -42,7 +41,6 @@ public sealed class SidecarProtocolHost
     ];
 
     private readonly Func<CancellationToken, Task<SidecarCapabilitiesDto>> _capabilitiesProvider;
-    private readonly PatternValidator _patternValidator;
     private readonly WorkflowValidator _workflowValidator;
     private readonly ITurnWorkflowRunner _workflowRunner;
     private readonly ICopilotSessionManager _sessionManager;
@@ -55,29 +53,26 @@ public sealed class SidecarProtocolHost
         new(StringComparer.Ordinal);
 
     public SidecarProtocolHost()
-        : this(new PatternValidator(), new WorkflowValidator())
+        : this(new WorkflowValidator())
     {
     }
 
     public SidecarProtocolHost(
-        PatternValidator patternValidator,
         ITurnWorkflowRunner? workflowRunner = null,
         Func<CancellationToken, Task<SidecarCapabilitiesDto>>? capabilitiesProvider = null,
         ICopilotSessionManager? sessionManager = null)
-        : this(patternValidator, new WorkflowValidator(), workflowRunner, capabilitiesProvider, sessionManager)
+        : this(new WorkflowValidator(), workflowRunner, capabilitiesProvider, sessionManager)
     {
     }
 
     public SidecarProtocolHost(
-        PatternValidator patternValidator,
         WorkflowValidator workflowValidator,
         ITurnWorkflowRunner? workflowRunner = null,
         Func<CancellationToken, Task<SidecarCapabilitiesDto>>? capabilitiesProvider = null,
         ICopilotSessionManager? sessionManager = null)
     {
-        _patternValidator = patternValidator;
         _workflowValidator = workflowValidator;
-        _workflowRunner = workflowRunner ?? new CopilotWorkflowRunner(_patternValidator, _workflowValidator);
+        _workflowRunner = workflowRunner ?? new CopilotWorkflowRunner(_workflowValidator);
         _capabilitiesProvider = capabilitiesProvider ?? BuildCapabilitiesAsync;
         _sessionManager = sessionManager ?? new CopilotSessionManager();
         _jsonOptions = JsonSerialization.CreateWebOptions();
@@ -86,7 +81,6 @@ public sealed class SidecarProtocolHost
         _commandHandlers = new Dictionary<string, Func<CommandContext, Task>>(StringComparer.Ordinal)
         {
             [DescribeCapabilitiesCommandType] = HandleDescribeCapabilitiesAsync,
-            [ValidatePatternCommandType] = HandleValidatePatternAsync,
             [ValidateWorkflowCommandType] = HandleValidateWorkflowAsync,
             [RunTurnCommandType] = HandleRunTurnAsync,
             [CancelTurnCommandType] = HandleCancelTurnAsync,
@@ -182,18 +176,6 @@ public sealed class SidecarProtocolHost
         }, context.CancellationToken).ConfigureAwait(false);
     }
 
-    private async Task HandleValidatePatternAsync(CommandContext context)
-    {
-        ValidatePatternCommandDto command = DeserializeCommand<ValidatePatternCommandDto>(context);
-
-        await WriteAsync(context.Output, new PatternValidationEventDto
-        {
-            Type = "pattern-validation",
-            RequestId = context.Envelope.RequestId,
-            Issues = _patternValidator.Validate(command.Pattern),
-        }, context.CancellationToken).ConfigureAwait(false);
-    }
-
     private async Task HandleValidateWorkflowAsync(CommandContext context)
     {
         ValidateWorkflowCommandDto command = DeserializeCommand<ValidateWorkflowCommandDto>(context);