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.go

@@ -835,6 +835,8 @@ func (db *DB) removeConversationScopedDirs(conversationID, projectID string) {
 	db.removeConversationScopedDir(db.einoPlantaskBaseDir, conversationID, "plantask")
 	// Eino ADK runner checkpoints (checkpoint_dir/<id>/).
 	db.removeConversationScopedDir(db.einoCheckpointBaseDir, conversationID, "eino_checkpoint")
+	// 上传附件始终归属单个会话，项目绑定的会话也要删，故放在 projectID 判断之外。
+	db.removeChatUploadDirs(conversationID)
 	// Eino reduction persisted tool outputs (tmp/reduction/conversations/<id>/).
 	// Project-bound sessions share projects/<id>/ — skip on single conversation delete.
 	if strings.TrimSpace(projectID) == "" {
@@ -845,6 +847,33 @@ func (db *DB) removeConversationScopedDirs(conversationID, projectID string) {
 	}
 }
 
+// removeChatUploadDirs 删除 chat_uploads/<日期>/<会话ID>/ 下属于该会话的上传目录。
+// 该根目录比其他产物多一层日期目录，无法复用 removeConversationScopedDir。
+func (db *DB) removeChatUploadDirs(conversationID string) {
+	base := strings.TrimSpace(db.chatUploadsDir)
+	if base == "" || strings.TrimSpace(conversationID) == "" {
+		return
+	}
+	seg := sanitizeConversationPathSegment(conversationID)
+	dates, err := os.ReadDir(base)
+	if err != nil {
+		return
+	}
+	for _, dateDir := range dates {
+		if !dateDir.IsDir() {
+			continue
+		}
+		dir := filepath.Join(base, dateDir.Name(), seg)
+		if rmErr := os.RemoveAll(dir); rmErr != nil && db.logger != nil {
+			db.logger.Warn("删除会话上传目录失败",
+				zap.String("conversationId", conversationID),
+				zap.String("kind", "chat_uploads"),
+				zap.String("dir", dir),
+				zap.Error(rmErr))
+		}
+	}
+}
+
 func (db *DB) removeProjectScopedDirs(projectID string) {
 	// Eino reduction persisted tool outputs (tmp/reduction/projects/<id>/).
 	reductionBase := filepath.Join(db.einoReductionBaseDir(), "projects")