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/appServiceWorkflowCheckpointing.test.ts

@@ -8,6 +8,7 @@ import {
   type RunTimelineEventRecord,
   type SessionRunRecord,
 } from '@shared/domain/runTimeline';
+import type { WorkflowDefinition } from '@shared/domain/workflow';
 
 mock.module('electron', () => {
   const electronMock = {
@@ -200,7 +201,7 @@ describe('AryxAppService workflow checkpointing', () => {
         workspaceKind: 'scratchpad',
         mode: 'interactive',
         messageMode: 'enqueue',
-        pattern: createPattern(),
+        workflow: createWorkflow(),
         messages: session.messages,
         resumeFromCheckpoint,
       }),
@@ -230,7 +231,7 @@ describe('AryxAppService workflow checkpointing', () => {
 });
 
 function createRunningSession(): { session: SessionRecord; run: SessionRunRecord } {
-  const pattern = createPattern();
+  const workflow = createWorkflow();
   const run = createSessionRunRecord({
     requestId: 'turn-1',
     project: {
@@ -239,14 +240,14 @@ function createRunningSession(): { session: SessionRecord; run: SessionRunRecord
     },
     workingDirectory: 'C:\\scratchpad',
     workspaceKind: 'scratchpad',
-    pattern,
+    workflow,
     triggerMessageId: 'msg-user-1',
     startedAt: '2026-04-01T12:00:00.000Z',
   });
   const session: SessionRecord = {
     id: 'session-1',
     projectId: SCRATCHPAD_PROJECT_ID,
-    patternId: pattern.id,
+    workflowId: workflow.id,
     title: 'Checkpoint session',
     createdAt: '2026-04-01T12:00:00.000Z',
     updatedAt: '2026-04-01T12:00:00.000Z',
@@ -274,23 +275,42 @@ function createRunningSession(): { session: SessionRecord; run: SessionRunRecord
   return { session, run };
 }
 
-function createPattern() {
+function createWorkflow(): WorkflowDefinition {
   return {
-    id: 'pattern-handoff',
+    id: 'workflow-handoff',
     name: 'Checkpointing flow',
     description: '',
-    mode: 'handoff' as const,
-    availability: 'available' as const,
-    maxIterations: 4,
-    agents: [
-      {
-        id: 'agent-1',
-        name: 'Primary',
-        description: '',
-        instructions: 'Help with the request.',
-        model: 'gpt-5.4',
-      },
-    ],
+    graph: {
+      nodes: [
+        { id: 'start', kind: 'start', label: 'Start', position: { x: 0, y: 0 }, config: { kind: 'start' } },
+        {
+          id: 'agent-1',
+          kind: 'agent',
+          label: 'Primary',
+          position: { x: 200, y: 0 },
+          order: 0,
+          config: {
+            kind: 'agent',
+            id: 'agent-1',
+            name: 'Primary',
+            description: '',
+            instructions: 'Help with the request.',
+            model: 'gpt-5.4',
+          },
+        },
+        { id: 'end', kind: 'end', label: 'End', position: { x: 400, y: 0 }, config: { kind: 'end' } },
+      ],
+      edges: [
+        { id: 'edge-start-agent', source: 'start', target: 'agent-1', kind: 'direct' },
+        { id: 'edge-agent-end', source: 'agent-1', target: 'end', kind: 'direct' },
+      ],
+    },
+    settings: {
+      checkpointing: { enabled: true },
+      executionMode: 'off-thread' as const,
+      orchestrationMode: 'handoff' as const,
+      maxIterations: 4,
+    },
     createdAt: '2026-04-01T00:00:00.000Z',
     updatedAt: '2026-04-01T00:00:00.000Z',
   };