git: discover worktrees when opening a worktree directory

When a worktree directory is opened with `git.detectWorktrees` enabled,
`checkForWorktrees()` previously returned early without discovering the
main repository or sibling worktrees. This left worktree management
commands non-functional because:

- Commands like "Create Worktree" filter for repository/submodule kind
- "Open Worktree" requires gitOpenRepositoryCount > 1
- SCM menu items depend on a repository-kind provider being open

Now, when a worktree is opened, `checkForWorktrees()` discovers and
opens sibling worktrees and the main repository (excluding the current
worktree from the candidate list). This enables the full worktree
management workflow regardless of which worktree is opened first.

The existing `isRepositoryOutsideWorkspace()` check already allows this
because it recognizes paths that appear in any open repository's worktree
list, and `getRepositoryExact()` prevents duplicate/recursive opens.

Also fixes a confusing log message that said detection "is not skipped"
when it was in fact skipping.

Fixes #264209

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

Author: marcelsafin

extensions/git/src/model.ts

@@ -807,17 +807,18 @@ export class Model implements IRepositoryResolver, IBranchProtectionProviderRegi
 				return;
 			}
 
-			if (repository.kind === 'worktree') {
-				this.logger.trace('[Model][open] Automatic detection of git worktrees is not skipped.');
-				return;
-			}
-
-			if (repository.worktrees.length > worktreesLimit) {
-				window.showWarningMessage(l10n.t('The "{0}" repository has {1} worktrees which won\'t be opened automatically. You can still open each one individually by opening a file within.', path.basename(repository.root), repository.worktrees.length));
+			// When a worktree is opened, discover sibling worktrees and the
+			// main repository so that worktree management commands are available.
+			const candidateWorktrees = repository.kind === 'worktree'
+				? repository.worktrees.filter(w => !pathEquals(w.path, repository.root))
+				: repository.worktrees;
+
+			if (candidateWorktrees.length > worktreesLimit) {
+				window.showWarningMessage(l10n.t('The "{0}" repository has {1} worktrees which won\'t be opened automatically. You can still open each one individually by opening a file within.', path.basename(repository.root), candidateWorktrees.length));
 				statusListener.dispose();
 			}
 
-			repository.worktrees
+			candidateWorktrees
 				.slice(0, worktreesLimit)
 				.forEach(w => {
 					this.logger.trace(`[Model][open] Opening worktree: '${w.path}'`);