fix(backend): configPath from THT_CONFIG env (routes senza workspace fallivano in container)

app.ts hardcodava configPath='config/tht.yaml' (symlink solo in dev). Nel container
i route che non passano workspace esplicito (sessionList/sessionShow/documents)
cercavano config/tht.yaml inesistente -> 500. Ora legge THT_CONFIG (entrypoint lo
setta a workspaces/local.yaml), fallback al default per dev. Compose lo esplicita.
Verificato: GET /sessions ora ritorna la lista.

compose.yaml

@@ -21,9 +21,9 @@ services:
       PORT: "8787"
       THT_HARNESS_DIR: /app/harness
       THT_BIN: /opt/venv/bin/tht
-      PI_BIN: pi
-      AUTH_MODE: ${AUTH_MODE:-none}
       SETTINGS_FILE: /data/settings/settings.json
+      THT_CONFIG: /app/harness/workspaces/local.yaml   # configPath di default per i route tht senza workspace esplicito
+      AUTH_MODE: ${AUTH_MODE:-none}
       MAX_PI_PROCESSES: ${MAX_PI_PROCESSES:-4}
     extra_hosts:
       - "host.docker.internal:host-gateway"   # Supabase :5438 + Ollama :11434 sull'host