Add agent task sessions table, session types, and programmatic DB backup

Add agent_task_sessions table for per-task session state keyed by
(agent, adapter, taskKey). Add AgentTaskSession type, resetAgentSessionSchema
validator, and sessionDisplayId/sessionParamsJson to AgentRuntimeState.

Rework migration hash-resolution fallback ordering to prefer hash-based
matching over timestamp-based journal matching. Move backup-db.sh logic
into packages/db/src/backup.ts for programmatic use and simplify the shell
script to call the TypeScript implementation.

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

packages/shared/src/index.ts

@@ -51,6 +51,7 @@ export type {
   HeartbeatRun,
   HeartbeatRunEvent,
   AgentRuntimeState,
+  AgentTaskSession,
   AgentWakeupRequest,
   LiveEvent,
   DashboardSummary,
@@ -68,6 +69,7 @@ export {
   updateAgentSchema,
   createAgentKeySchema,
   wakeAgentSchema,
+  resetAgentSessionSchema,
   agentPermissionsSchema,
   updateAgentPermissionsSchema,
   type CreateAgent,
@@ -75,6 +77,7 @@ export {
   type UpdateAgent,
   type CreateAgentKey,
   type WakeAgent,
+  type ResetAgentSession,
   type UpdateAgentPermissions,
   createProjectSchema,
   updateProjectSchema,