feat(session): persist model tier overrides per session

Store per-session config in SQLite and route /model and /reset through command fast-paths so channel sessions keep independent model selection across reconnects and restarts.

src/audit/types.ts

@@ -3,6 +3,8 @@ export type AuditLevel = 'debug' | 'info' | 'warn' | 'error';
 export type AuditEventType =
   // Tool execution
   | 'tool.start' | 'tool.success' | 'tool.error' | 'tool.denied'
+  // Skills installer
+  | 'skills.installer.execution_blocked' | 'skills.installer.command_result'
   // Session lifecycle
   | 'session.create' | 'session.message' | 'session.delete' | 'session.transfer' | 'session.compact'
   // Automation - Cron
@@ -75,6 +77,24 @@ export interface ToolDeniedEvent {
   denial_type: 'policy' | 'hook' | 'not_found' | 'autonomy_override';
 }
 
+export interface SkillsInstallerExecutionBlockedEvent {
+  skill_name: string;
+  phase: 'install' | 'execute';
+  execution_requested: boolean;
+  execution_enabled: boolean;
+  reason: string;
+  attempted_command_count: number;
+}
+
+export interface SkillsInstallerCommandResultEvent {
+  skill_name: string;
+  phase: 'install' | 'execute';
+  installer_type: string;
+  command: string;
+  status: 'blocked' | 'skipped' | 'succeeded' | 'failed';
+  reason: string;
+}
+
 export interface SessionCreateEvent {
   session_id: string;
   frontend: string;