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>

tests/main/appServiceWorkflow.test.ts

@@ -87,11 +87,13 @@ function createWorkflow(): WorkflowDefinition {
 describe('AryxAppService workflow operations', () => {
   test('saves workflows into workspace state', async () => {
     const workspace = createWorkspaceSeed();
+    const initialWorkflowCount = workspace.workflows.length;
     const service = createService(workspace);
 
     const result = await service.saveWorkflow(createWorkflow());
 
-    expect(result.workflows).toHaveLength(1);
+    expect(result.workflows).toHaveLength(initialWorkflowCount + 1);
+    expect(result.workflows.some((workflow) => workflow.id === 'workflow-test')).toBe(true);
     expect(result.selectedWorkflowId).toBe('workflow-test');
   });
 
@@ -115,40 +117,28 @@ describe('AryxAppService workflow operations', () => {
 
   test('creates workflows from templates and selects the new workflow', async () => {
     const workspace = createWorkspaceSeed();
+    const initialWorkflowCount = workspace.workflows.length;
     const service = createService(workspace);
 
     const result = await service.createWorkflowFromTemplate('workflow-template-code-review', {
       name: 'Template Copy',
     });
 
-    expect(result.workflows).toHaveLength(1);
-    expect(result.workflows[0]?.name).toBe('Template Copy');
-    expect(result.selectedWorkflowId).toBe(result.workflows[0]?.id);
-  });
-
-  test('upgrades a pattern to a saved workflow without removing the pattern', async () => {
-    const workspace = createWorkspaceSeed();
-    const pattern = workspace.patterns.find((candidate) => candidate.mode === 'handoff');
-    if (!pattern) {
-      throw new Error('Expected a handoff pattern.');
-    }
-
-    const service = createService(workspace);
-    const result = await service.upgradePatternToWorkflow(pattern.id, { save: true });
-
-    expect(result.workspace?.workflows).toHaveLength(1);
-    expect(result.workspace?.patterns.some((candidate) => candidate.id === pattern.id)).toBe(true);
-    expect(result.workflow.id).toBe('workflow-handoff-support');
+    expect(result.workflows).toHaveLength(initialWorkflowCount + 1);
+    const createdWorkflow = result.workflows.find((workflow) => workflow.name === 'Template Copy');
+    expect(createdWorkflow).toBeDefined();
+    expect(result.selectedWorkflowId).toBe(createdWorkflow?.id);
   });
 
   test('imports and saves workflows from yaml', async () => {
     const workspace = createWorkspaceSeed();
+    const initialWorkflowCount = workspace.workflows.length;
     const service = createService(workspace);
     const yaml = exportWorkflowDefinition(createWorkflow(), 'yaml').content;
 
     const result = await service.importWorkflow(yaml, 'yaml', { save: true });
 
-    expect(result.workspace?.workflows).toHaveLength(1);
+    expect(result.workspace?.workflows).toHaveLength(initialWorkflowCount + 1);
     expect(result.workspace?.selectedWorkflowId).toBe('workflow-test');
     expect(result.workflow.id).toBe('workflow-test');
   });