refactor(core): codebase quality cleanup

- Remove user-level model settings (chat_model_id, memory_model_id,
  embedding_model_id, max_context_load_time, language) from users table
- Merge migration 0002 into 0001, remove compatibility migrations
- Delete dead conversation/resolver.go (1177 lines, only flow/resolver.go used)
- Remove type aliases (Chat=Conversation, types_alias.go)
- Fix SQL: remove AND false stub, fix UpdateChatTitle model_id,
  reset model IDs in DeleteSettings, add preauth expiry filter,
  add ListMessages limit, remove 10 dead queries
- Extract shared handler helpers (RequireChannelIdentityID, AuthorizeBotAccess)
- Rename internal/router to internal/channel/inbound
- Fix identity confusion: remove UserID->ChannelIdentityID fallbacks
- Fix all _ = var patterns with proper error logging
- Fix error propagation: storeMessages, rescheduleJob, botContainerID
- Fix naming: ModelId->ModelID, active->is_active, Duration semantic fix
- Remove dead code: mcpService, ReplyTarget, callMCPServer, sshShellQuote,
  buildSessionMetadata, ChatRequest.Language, TriggerPayload.ChatID
- Fix code quality: errors.Is(), remove goto, CreateHuman deprecated
- Remove Enable model endpoint and user-level settings CLI commands
- Regenerate sqlc, swagger, SDK

db/queries/users.sql

@@ -8,13 +8,6 @@ SELECT *
 FROM users
 WHERE id = $1;
 
--- name: UpdateUserStatus :one
-UPDATE users
-SET is_active = $2,
-    updated_at = now()
-WHERE id = $1
-RETURNING *;
-
 -- name: CreateAccount :one
 UPDATE users
 SET username = sqlc.arg(username),
@@ -54,9 +47,6 @@ ON CONFLICT (username) DO UPDATE SET
   updated_at = now()
 RETURNING *;
 
--- name: GetAccountByUsername :one
-SELECT * FROM users WHERE username = sqlc.arg(username);
-
 -- name: GetAccountByIdentity :one
 SELECT * FROM users WHERE username = sqlc.arg(identity) OR email = sqlc.arg(identity);