feat: add git workflow frontend components

- RunChangeSummaryCard: post-run change review card with expandable
  file diffs, origin badges, selective discard with confirmation,
  and commit composer launch button
- CommitComposer: slide-over panel for staging files, editing AI-
  suggested commit messages, conventional commit type selection,
  and commit with optional push
- GitPanel: embedded activity panel section with branch management,
  push/pull/fetch operations, working tree inspection with inline
  diffs, and recent commit history
- Wire RunChangeSummaryCard into RunTimeline after completed runs
- Wire CommitComposer as overlay in App.tsx with state management
- Wire GitPanel into ActivityPanel for non-scratchpad sessions
- Update ARCHITECTURE.md with frontend git integration description

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

src/renderer/components/ActivityPanel.tsx

@@ -1,5 +1,5 @@
 import { useMemo, type ReactNode } from 'react';
-import { Activity, ArrowRight, BarChart3, CheckCircle2, Clock, Cog, ShieldAlert, Sparkles, Users, Zap } from 'lucide-react';
+import { Activity, ArrowRight, BarChart3, CheckCircle2, Clock, Cog, GitBranch as GitBranchIcon, ShieldAlert, Sparkles, Users, Zap } from 'lucide-react';
 
 import {
   buildAgentActivityRows,
@@ -16,8 +16,11 @@ import {
   type TurnEventLog,
 } from '@renderer/lib/sessionActivity';
 import { RunTimeline } from '@renderer/components/RunTimeline';
+import { GitPanel } from '@renderer/components/GitPanel';
 import { inferProvider } from '@shared/domain/models';
 import type { OrchestrationMode, PatternAgentDefinition, PatternDefinition } from '@shared/domain/pattern';
+import { isScratchpadProject } from '@shared/domain/project';
+import type { ProjectGitFileReference } from '@shared/domain/project';
 import type { SessionRecord } from '@shared/domain/session';
 import { ProviderIcon } from './ProviderIcons';
 
@@ -208,6 +211,8 @@ function formatTurnEventTimestamp(iso: string): string {
 interface ActivityPanelProps {
   activity?: SessionActivityState;
   onJumpToMessage?: (messageId: string) => void;
+  onDiscard?: (sessionId: string, runId: string, files?: ProjectGitFileReference[]) => Promise<unknown>;
+  onOpenCommitComposer?: () => void;
   pattern: PatternDefinition;
   session: SessionRecord;
   sessionRequestUsage?: SessionRequestUsageState;
@@ -217,6 +222,8 @@ interface ActivityPanelProps {
 export function ActivityPanel({
   activity,
   onJumpToMessage,
+  onDiscard,
+  onOpenCommitComposer,
   pattern,
   session,
   sessionRequestUsage,
@@ -345,7 +352,13 @@ export function ActivityPanel({
             )}
           </SectionHeader>
 
-          <RunTimeline onJumpToMessage={onJumpToMessage} runs={session.runs} />
+          <RunTimeline
+            onDiscard={onDiscard}
+            onJumpToMessage={onJumpToMessage}
+            onOpenCommitComposer={onOpenCommitComposer}
+            runs={session.runs}
+            sessionId={session.id}
+          />
         </div>
 
         {/* ── Turn events section ─────────────────────────── */}
@@ -382,6 +395,18 @@ export function ActivityPanel({
           </div>
         )}
 
+        {/* ── Git panel section ────────────────────────────── */}
+        {!isScratchpadProject(session.projectId) && (
+          <div className="mb-4">
+            <SectionHeader>
+              <GitBranchIcon className="size-3" />
+              <span>Git</span>
+            </SectionHeader>
+
+            <GitPanel projectId={session.projectId} />
+          </div>
+        )}
+
       </div>
     </div>
   );