Move worktrees to ~/.Conclave to avoid Windows MAX_PATH issues

src/Conclave.App/Sessions/Database.cs

@@ -160,6 +160,17 @@ public static string DefaultPath()
         return System.IO.Path.Combine(dir, "conclave.db");
     }
 
+    // Worktrees live under ~/.Conclave on every platform — separate from the app-data
+    // directory (which on Windows sits inside AppData\Roaming\Conclave) so per-file paths
+    // stay clear of Windows' 260-char MAX_PATH limit. Every saved character matters: the
+    // 32-char project id and slug already cost ~40, and git itself appends paths like
+    // ".git/worktrees/<name>/index.lock" inside the linked worktree.
+    public static string DefaultWorktreeRoot()
+    {
+        var home = Environment.GetFolderPath(Environment.SpecialFolder.UserProfile);
+        return System.IO.Path.Combine(home, ".Conclave");
+    }
+
     public static long Now() => DateTimeOffset.UtcNow.ToUnixTimeMilliseconds();
 
     private void Migrate()

src/Conclave.App/Sessions/SessionManager.cs

@@ -50,8 +50,7 @@ public static SessionManager Open(Tokens tokens)
     {
         var dbPath = Database.DefaultPath();
         var db = Database.Open(dbPath);
-        var root = Path.Combine(Path.GetDirectoryName(dbPath)!, "worktrees");
-        return new SessionManager(db, root, tokens);
+        return new SessionManager(db, Database.DefaultWorktreeRoot(), tokens);
     }
 
     // --- Loading ---

src/Conclave.App/ViewModels/NewSessionVm.cs

@@ -91,7 +91,7 @@ public string WorktreePath
             var slug = DeriveSlug(_branch);
             if (_project.IsFusion)
                 return $"{_project.MemberIds.Count} worktrees · {slug}";
-            return $"worktrees/{_project.Id[..8]}/{slug}";
+            return $"~/.Conclave/{_project.Id[..8]}/{slug}";
         }
     }