feat: add libSQL/Turso database backend with full feature parity

Introduce a Database trait abstraction (~60 async methods) enabling
compile-time backend selection between PostgreSQL and libSQL/Turso.
Convert all modules from concrete Store to Arc<dyn Database>, add
LibSqlSecretsStore and LibSqlWasmToolStore implementations, wire
libsql stores throughout CLI and main entry points, and make the
setup wizard backend-agnostic.

Key changes:
- src/db/: Database trait, PostgresDatabase adapter, LibSqlBackend
  with native SQLite-dialect SQL, and idempotent migration system
- src/secrets/store.rs: LibSqlSecretsStore (all 8 trait methods)
- src/tools/wasm/storage.rs: LibSqlWasmToolStore (all 7 trait methods)
- src/main.rs, cli/tool.rs, cli/mcp.rs: backend-conditional wiring
- src/setup/channels.rs: SecretsContext uses Arc<dyn SecretsStore>
- Feature-gate postgres-only tests and examples

Co-Authored-By: Claude Opus 4.6 <[email protected]>

src/orchestrator/api.rs

@@ -15,7 +15,7 @@ use tokio::sync::{Mutex, broadcast};
 use uuid::Uuid;
 
 use crate::channels::web::types::SseEvent;
-use crate::history::Store;
+use crate::db::Database;
 use crate::llm::{CompletionRequest, LlmProvider, ToolCompletionRequest};
 use crate::orchestrator::auth::{TokenStore, worker_auth_middleware};
 use crate::orchestrator::job_manager::ContainerJobManager;
@@ -43,7 +43,7 @@ pub struct OrchestratorState {
     /// Buffered follow-up prompts for sandbox jobs, keyed by job_id.
     pub prompt_queue: Arc<Mutex<HashMap<Uuid, VecDeque<PendingPrompt>>>>,
     /// Database handle for persisting job events.
-    pub store: Option<Arc<Store>>,
+    pub store: Option<Arc<dyn Database>>,
 }
 
 /// The orchestrator's internal API server.