feat: per-group queue, SQLite state, graceful shutdown

Add per-group container locking with global concurrency limit to prevent
concurrent containers for the same group (#89) and cap total containers.
Fix message batching bug where lastAgentTimestamp advanced to trigger
message instead of latest in batch, causing redundant re-processing.
Move router state, sessions, and registered groups from JSON files to
SQLite with automatic one-time migration. Add SIGTERM/SIGINT handlers
with graceful shutdown (SIGTERM -> grace period -> SIGKILL). Add startup
recovery for messages missed during crash. Remove dead code: utils.ts,
Session type, isScheduledTask flag, ContainerConfig.env, getTaskRunLogs,
GroupQueue.isActive.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/types.ts

@@ -30,7 +30,6 @@ export interface AllowedRoot {
 export interface ContainerConfig {
   additionalMounts?: AdditionalMount[];
   timeout?: number; // Default: 300000 (5 minutes)
-  env?: Record<string, string>;
 }
 
 export interface RegisteredGroup {
@@ -41,10 +40,6 @@ export interface RegisteredGroup {
   containerConfig?: ContainerConfig;
 }
 
-export interface Session {
-  [folder: string]: string;
-}
-
 export interface NewMessage {
   id: string;
   chat_jid: string;