test(source-control): harden identity-row detached + no-identity contracts

Add a stable data-testid to the identity row so the no-identity case proves no
row renders, and assert the detached badge's accessible label + focusability.
Addresses CodeRabbit review on #10215.

src/renderer/src/components/right-sidebar/source-control-header-toolbar-identity.test.tsx

@@ -74,6 +74,7 @@ describe('SourceControlHeaderToolbar branch identity', () => {
     const createPrIndex = markup.indexOf('Create PR')
 
     // Why: the #9787 revert regression — identity must not evict Create PR.
+    expect(markup).toContain('data-testid="source-control-git-identity-row"')
     expect(branchIndex).toBeGreaterThan(-1)
     expect(createPrIndex).toBeGreaterThan(-1)
     // Identity row renders above the toolbar row that hosts Create PR.
@@ -94,13 +95,20 @@ describe('SourceControlHeaderToolbar branch identity', () => {
     })
 
     expect(markup).not.toContain('aria-label="Current branch:')
+    expect(markup).toContain('data-testid="source-control-git-identity-row"')
     expect(markup).toContain('Detached HEAD · 8cec248')
+    // Detached badge stays keyboard-reachable and exposes the full tooltip as its label.
+    expect(markup).toContain(
+      'aria-label="Detached HEAD at 8cec248. You are viewing a commit, not a branch."'
+    )
+    expect(markup).toContain('tabindex="0"')
     expect(markup).toContain('Create PR')
   })
 
   it('omits the identity row when there is no git identity', () => {
     const markup = renderToolbar({ gitIdentityDisplay: null })
 
+    expect(markup).not.toContain('data-testid="source-control-git-identity-row"')
     expect(markup).not.toContain('aria-label="Current branch:')
     expect(markup).toContain('Create PR')
   })

src/renderer/src/components/right-sidebar/source-control-header-toolbar.tsx

@@ -55,7 +55,7 @@ function SourceControlGitIdentityRow({
 }): React.JSX.Element {
   if (display.kind === 'detached') {
     return (
-      <div className="mb-1 flex min-w-0 items-center">
+      <div data-testid="source-control-git-identity-row" className="mb-1 flex min-w-0 items-center">
         <DetachedHeadBadge
           display={display}
           side="bottom"
@@ -74,7 +74,7 @@ function SourceControlGitIdentityRow({
   )
 
   return (
-    <div className="mb-1 flex min-w-0 items-center">
+    <div data-testid="source-control-git-identity-row" className="mb-1 flex min-w-0 items-center">
       <Tooltip>
         <TooltipTrigger asChild>
           <span