feat: add runtime storage cleanup with per-category retention (#310) (#313)

Runtime artifacts (agent workspaces, tool-output spill, C2 payloads, chat
uploads, workflow checkpoints, diagnostic logs) previously accumulated
without bound: most were only removed when a conversation or project was
deleted, and tmp/c2 plus workflow checkpoints were never removed at all.

Add a storage cleaner with named per-category tasks (Gitea-style), a
settings page tab, and a background sweep that is off by default so
upgrading never deletes existing data.

Safety properties, since mis-deleting live task data costs far more than
the disk saved:
- dry-run is the default; a real cleanup requires dry_run=false together
  with confirm=true at the API layer, not just a frontend dialog
- sessions active within active_grace_hours are always skipped, and a
  failed activity lookup skips conservatively (fail closed)
- directories whose conversation/project no longer exists are reclaimed
  as orphans after orphan_grace_days
- scanners never follow symlinks and every candidate path is confined to
  its category root; deletion renames to a .tmp-for-deletion marker first
  so a crash leaves recoverable residue instead of a half-deleted dir
- storage:* permissions are admin-only; without the grantSystemRolePermissions
  skip the default branch would have given operators an irreversible
  file-deletion right

Also fix two confirmed leaks: DeleteConversation left chat_uploads files
on disk (their rows already vanished via ON DELETE CASCADE), and workflow
checkpoints had no deletion path at all.

Co-authored-by: Parallels <parallels@kali-linux-2025-2.localdomain>

internal/database/conversation_cleanup_test.go

@@ -60,6 +60,67 @@ func TestDeleteConversationRemovesEinoScopedDirs(t *testing.T) {
 	}
 }
 
+// chat_uploads 比其他产物多一层日期目录（chat_uploads/<日期>/<会话ID>），
+// 历史上删除会话只清了数据库行（ON DELETE CASCADE），磁盘文件会永久残留。
+func TestDeleteConversationRemovesChatUploads(t *testing.T) {
+	tmp := t.TempDir()
+	dbPath := filepath.Join(tmp, "conversations.db")
+	db, err := NewDB(dbPath, zap.NewNop())
+	if err != nil {
+		t.Fatalf("NewDB: %v", err)
+	}
+	defer db.Close()
+
+	uploads := filepath.Join(tmp, "chat_uploads")
+	db.SetChatUploadsDir(uploads)
+
+	target, err := db.CreateConversation("uploads cleanup", ConversationCreateMeta{})
+	if err != nil {
+		t.Fatalf("CreateConversation: %v", err)
+	}
+	sibling, err := db.CreateConversation("sibling", ConversationCreateMeta{})
+	if err != nil {
+		t.Fatalf("CreateConversation: %v", err)
+	}
+	targetSeg := sanitizeConversationPathSegment(target.ID)
+	siblingSeg := sanitizeConversationPathSegment(sibling.ID)
+
+	// 同一会话跨两个日期目录都有上传件，另一个会话的上传件必须保留。
+	for _, dir := range []string{
+		filepath.Join(uploads, "2026-06-01", targetSeg),
+		filepath.Join(uploads, "2026-06-02", targetSeg),
+		filepath.Join(uploads, "2026-06-01", siblingSeg),
+	} {
+		if err := os.MkdirAll(dir, 0o755); err != nil {
+			t.Fatalf("mkdir %s: %v", dir, err)
+		}
+		if err := os.WriteFile(filepath.Join(dir, "report.pdf"), []byte("x"), 0o644); err != nil {
+			t.Fatalf("write %s: %v", dir, err)
+		}
+	}
+
+	if err := db.DeleteConversation(target.ID); err != nil {
+		t.Fatalf("DeleteConversation: %v", err)
+	}
+
+	for _, date := range []string{"2026-06-01", "2026-06-02"} {
+		dir := filepath.Join(uploads, date, targetSeg)
+		if _, statErr := os.Stat(dir); !os.IsNotExist(statErr) {
+			t.Errorf("expected removed dir %s, stat err=%v", dir, statErr)
+		}
+	}
+	siblingDir := filepath.Join(uploads, "2026-06-01", siblingSeg)
+	if _, statErr := os.Stat(filepath.Join(siblingDir, "report.pdf")); statErr != nil {
+		t.Errorf("其他会话的上传件被误删: %v", statErr)
+	}
+	if _, statErr := os.Stat(uploads); statErr != nil {
+		t.Errorf("chat_uploads 根目录不应被删除: %v", statErr)
+	}
+	if _, statErr := os.Stat(filepath.Join(uploads, "2026-06-01")); statErr != nil {
+		t.Errorf("仍有数据的日期目录不应被删除: %v", statErr)
+	}
+}
+
 func TestDeleteProjectRemovesReductionDir(t *testing.T) {
 	tmp := t.TempDir()
 	dbPath := filepath.Join(tmp, "conversations.db")