Identify the current and main worktree by git dir, not by path

`git worktree list` reports the main worktree as the common git dir with
a trailing "/.git" removed, which equals the working tree only when the
git dir sits inside it. In a submodule, a bare repo, or a repo using
core.worktree it doesn't, so comparing the reported path against the
working tree path matches nothing: no worktree is recognized as current
or as main. Most visibly, inside a submodule lazygit claimed we were in
a linked worktree named after the submodule, and offered to remove that
"worktree".

Comparing git dirs identifies a worktree unambiguously, so use that.
A worktree whose directory is gone has no git dir to compare, and there
we still have nothing better than its path.

The submodule tests were asserting the linked-worktree suffix in the
status view; it is gone now, and the repo name still says which
submodule we're in.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

pkg/integration/tests/submodule/enter.go

@@ -29,7 +29,7 @@ var Enter = NewIntegrationTest(NewIntegrationTestArgs{
 			t.Views().Status().Content(Contains("repo"))
 		}
 		assertInSubmodule := func() {
-			t.Views().Status().Content(Contains("my_submodule_path(my_submodule_name)"))
+			t.Views().Status().Content(Contains("my_submodule_path"))
 		}
 
 		assertInParentRepo()

pkg/integration/tests/submodule/enter_nested.go

@@ -37,7 +37,7 @@ var EnterNested = NewIntegrationTest(NewIntegrationTestArgs{
 			// enter the nested submodule
 			PressEnter()
 
-		t.Views().Status().Content(Contains("innerSubPath(innerSubName)"))
+		t.Views().Status().Content(Contains("innerSubPath"))
 		t.Views().Commits().ContainsLines(
 			Contains("initial inner commit"),
 		)

pkg/integration/tests/submodule/reset.go

@@ -31,7 +31,7 @@ var Reset = NewIntegrationTest(NewIntegrationTestArgs{
 			t.Views().Status().Content(Contains("repo"))
 		}
 		assertInSubmodule := func() {
-			t.Views().Status().Content(Contains("my_submodule_path(my_submodule_name)"))
+			t.Views().Status().Content(Contains("my_submodule_path"))
 		}
 
 		assertInParentRepo()