refactor: remove standalone mode, consolidate to managed-only (PostgreSQL) (#70)

- Remove standalone mode code: file-based stores, standalone gateway,
  heartbeat service, SQLite memory, standalone docker-compose
- Rename docker-compose.managed.yml → docker-compose.postgres.yml
- Clean up ~130 Go comments referencing "managed mode" qualifier
- Simplify docker-compose.yml env vars (providers/channels via web UI)
- Update .env.example to essential vars only (token + encryption key)
- Add setup wizard UI (provider → agent → channel bootstrap flow)
- Add logs.tail WebSocket handler for live log streaming
- Add cursor-pointer to interactive UI components
- Clean up config page (remove standalone-only sections)
- Update README and docs for managed-only architecture

pkg/protocol/methods.go

@@ -83,7 +83,7 @@ const (
 	MethodSend = "send"
 )
 
-// Channel instances management (managed mode)
+// Channel instances management
 const (
 	MethodChannelInstancesList   = "channels.instances.list"
 	MethodChannelInstancesGet    = "channels.instances.get"
@@ -92,7 +92,7 @@ const (
 	MethodChannelInstancesDelete = "channels.instances.delete"
 )
 
-// Agent links (inter-agent delegation, managed mode)
+// Agent links (inter-agent delegation)
 const (
 	MethodAgentsLinksList   = "agents.links.list"
 	MethodAgentsLinksCreate = "agents.links.create"
@@ -100,7 +100,7 @@ const (
 	MethodAgentsLinksDelete = "agents.links.delete"
 )
 
-// Agent teams (managed mode)
+// Agent teams
 const (
 	MethodTeamsList     = "teams.list"
 	MethodTeamsCreate   = "teams.create"
@@ -113,7 +113,7 @@ const (
 	MethodTeamsKnownUsers    = "teams.known_users"
 )
 
-// Delegation history (managed mode)
+// Delegation history
 const (
 	MethodDelegationsList = "delegations.list"
 	MethodDelegationsGet  = "delegations.get"
@@ -134,9 +134,7 @@ const (
 	MethodBrowserSnapshot   = "browser.snapshot"
 	MethodBrowserScreenshot = "browser.screenshot"
 
-	MethodHeartbeat = "heartbeat"
-
-	// Zalo Personal (managed mode)
+	// Zalo Personal
 	MethodZaloPersonalQRStart   = "zalo.personal.qr.start"
 	MethodZaloPersonalContacts  = "zalo.personal.contacts"
 )