fix: harden pi maintenance lifecycle

backend/src/config.ts

@@ -12,6 +12,7 @@ export interface AppConfig {
   defaults: { provider?: string; model?: string; thinking?: string };
   maxPiProcesses: number;
   settingsFile: string;
+  maintenanceFile: string;
   dataRoot?: string;
   ollamaEnsureTimeoutMs: number;
   secretsFile?: string;
@@ -206,6 +207,7 @@ export function loadConfig(env: Record<string, string | undefined>): AppConfig {
     defaults: { provider: env.PI_PROVIDER, model: env.PI_MODEL, thinking: env.PI_THINKING },
     maxPiProcesses: Number(env.MAX_PI_PROCESSES ?? 4),
     settingsFile: env.SETTINGS_FILE ?? "data/settings.json",
+    maintenanceFile: env.THT_MAINTENANCE_FILE ?? "data/maintenance.json",
     dataRoot: env.THT_DATA_ROOT,
     ollamaEnsureTimeoutMs: Number(env.OLLAMA_ENSURE_TIMEOUT_MS ?? 60000),
     secretsFile,