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>

src/renderer/components/chat/InlinePills.tsx

@@ -556,7 +556,7 @@ export function InlineApprovalPill({
 
       {open && !disabled && (
         <div className="absolute bottom-full left-0 z-40 mb-1.5 max-h-[28rem] w-80 overflow-y-auto rounded-lg border border-[var(--color-border)] bg-[var(--color-surface-1)] shadow-2xl">
-          {/* Header: session override / pattern defaults */}
+          {/* Header: session override / workflow defaults */}
           <div className="sticky top-0 z-10 border-b border-[var(--color-border)] bg-[var(--color-surface-1)]">
             <div className="flex items-center gap-2 px-3 py-2">
               <span className={`rounded-full px-2 py-0.5 text-[9px] font-semibold uppercase tracking-wider ${

src/renderer/components/settings/WorkspaceAgentEditor.tsx

@@ -3,7 +3,7 @@ import { ModelSelect, ReasoningEffortSelect } from '@renderer/components/AgentCo
 import { findModel, type ModelDefinition } from '@shared/domain/models';
 import { resolveReasoningEffort } from '@shared/domain/models';
 import type { WorkspaceAgentDefinition } from '@shared/domain/workspaceAgent';
-import type { PatternDefinition } from '@shared/domain/pattern';
+import type { WorkflowDefinition } from '@shared/domain/workflow';
 import { findWorkspaceAgentUsages } from '@shared/domain/workspaceAgent';
 import { ToolingEditorShell } from './ToolingEditorShell';
 import { Link2, Workflow } from 'lucide-react';
@@ -21,7 +21,7 @@ export function WorkspaceAgentEditor({
   onSave,
   onDelete,
   availableModels,
-  patterns,
+  workflows,
 }: {
   agent: WorkspaceAgentDefinition;
   onChange: (agent: WorkspaceAgentDefinition) => void;
@@ -29,10 +29,10 @@ export function WorkspaceAgentEditor({
   onSave: () => Promise<void>;
   onDelete?: () => Promise<void>;
   availableModels: ReadonlyArray<ModelDefinition>;
-  patterns: PatternDefinition[];
+  workflows: WorkflowDefinition[];
 }) {
   const validationError = validateWorkspaceAgent(agent);
-  const usages = findWorkspaceAgentUsages(agent.id, patterns);
+  const usages = findWorkspaceAgentUsages(agent.id, workflows);
 
   return (
     <ToolingEditorShell
@@ -117,22 +117,22 @@ export function WorkspaceAgentEditor({
             {usages.map((usage) => (
               <div
                 className="flex items-center gap-2.5 border-b border-[var(--color-border)] px-3.5 py-2.5 last:border-b-0"
-                key={usage.patternId}
+                key={usage.workflowId}
               >
                 <Workflow className="size-3.5 shrink-0 text-[var(--color-text-muted)]" />
                 <span className="text-[13px] text-[var(--color-text-secondary)]">
-                  {usage.patternName}
+                  {usage.workflowName}
                 </span>
                 <Link2 className="ml-auto size-3 text-[var(--color-accent)]" />
               </div>
             ))}
           </div>
           <p className="text-[11px] text-[var(--color-text-muted)]">
-            Referenced by {usages.length} pattern{usages.length === 1 ? '' : 's'}.
-            Changes to this agent will affect all linked patterns.
-          </p>
-        </section>
-      )}
+             Referenced by {usages.length} workflow{usages.length === 1 ? '' : 's'}.
+             Changes to this agent will affect all linked workflows.
+           </p>
+         </section>
+       )}
     </ToolingEditorShell>
   );
 }