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/database.go

@@ -53,6 +53,7 @@ type DB struct {
 	einoCheckpointBaseDir    string // checkpoint_dir root (per-conversation subdirs)
 	einoReductionRootDir     string // reduction_root_dir or default tmp/reduction (conversations/<id> subdirs)
 	einoWorkspaceRootDir     string // workspace_root_dir or default tmp/workspace (projects|conversations/<id> subdirs)
+	chatUploadsDir           string // chat_uploads root (<date>/<conversationID> subdirs)
 	checkpointLoopName       string
 	checkpointStop           chan struct{}
 	checkpointDone           chan struct{}
@@ -178,6 +179,16 @@ func (db *DB) SetEinoConversationDirs(plantaskBase, checkpointBase, reductionRoo
 	db.einoWorkspaceRootDir = strings.TrimSpace(workspaceRoot)
 }
 
+// SetChatUploadsDir configures the chat_uploads root so DeleteConversation can remove
+// uploaded attachment files. Their chat_upload_artifacts rows already disappear via
+// ON DELETE CASCADE; without this the files themselves would linger forever.
+func (db *DB) SetChatUploadsDir(dir string) {
+	if db == nil {
+		return
+	}
+	db.chatUploadsDir = strings.TrimSpace(dir)
+}
+
 // initTables 初始化数据库表
 func (db *DB) initTables() error {
 	// 创建对话表（last_react_input / last_react_output 存「代理消息轨迹」JSON 与助手摘要，列名保留以兼容已有库）