fix(git): silence getWorktrees warning when directory is not a repo

`getWorktrees` logs a warn-level line every time the managed OpenCode
process or any other caller passes a directory that is not inside a
git repository. The OpenChamber desktop main.log fills with hundreds
of these "Failed to list worktrees, returning empty list: fatal: not
a git repository ..." entries over a normal session.

The empty-list fallback is already correct (worktrees are an optional
feature), but the warning is noise that hides real git failures. Use
the existing `isNotGitRepositoryError` helper to suppress the warn
specifically for the "not a git repository" case and keep the
warning for genuine failures (lock contention, permission errors,
corrupt repos, etc.).

packages/web/server/lib/git/service.js

@@ -3738,7 +3738,15 @@ export async function getWorktrees(directory) {
       path: entry.worktree,
     }));
   } catch (error) {
-    console.warn('Failed to list worktrees, returning empty list:', error?.message || error);
+    // Worktrees are an optional feature. When the caller passes a directory
+    // that is not inside any git repository (for example, the managed
+    // OpenCode's working directory or an unconfigured project path), git
+    // exits with "fatal: not a git repository ...". Treat that as an
+    // authoritative empty result so the route handler can still respond
+    // 200 [] and the desktop main.log stays free of noise.
+    if (!isNotGitRepositoryError(error)) {
+      console.warn('Failed to list worktrees, returning empty list:', error?.message || error);
+    }
     return [];
   }
 }