fix: register data source for seed-demo market observations (#1257)

* fix: wire deposit/withdrawal saga orchestration in unified binary

The unified binary's wireCurrentAccount used the basic NewService()
constructor which creates a Service without deposit/withdrawal
orchestrators, causing nil pointer panics on ExecuteDeposit calls.

Switch to NewServiceWithExistingClients() with loopback gRPC clients
for position-keeping and financial-accounting, enabling full Starlark
saga orchestration within the unified binary.

Also:
- Copy saga script assets into Docker image (SAGA_ASSET_DIR=/app)
- Fix init-databases.sql: meridian_internal_account → meridian_internal_bank_account

* fix: load clearing account config from env for deposit double-entry

Without a clearing account, the deposit saga only creates a CREDIT
posting (to customer). FA rejects the unbalanced booking log. Load
AccountConfig from DEPOSIT_CLEARING_ACCOUNT_ID env var so the saga
creates both DEBIT (clearing) and CREDIT (customer) postings.

Gracefully falls back to nil when env var is unset.

* fix: fail fast on invalid clearing account config

Differentiate "env var not set" (graceful skip) from "env var set but
invalid" (hard error) to avoid silently falling back to single-sided
postings when config is misconfigured.

* fix: use account_id for PK position logs in deposit and withdrawal sagas

The Starlark deposit and withdrawal scripts were passing
external_identifier (e.g. VE-GBP-010) as the position_id to
position_keeping.initiate_log, but the post-deposit balance query
uses account_id (e.g. ACC-xxx). This mismatch caused PK balance
lookups to fail with "no position logs found for account".

* fix: add required CEL expressions to seed-demo dataset registration

RegisterDataSet now requires validation_expression and
resolution_key_expression fields. Add appropriate CEL expressions
for the wholesale energy price dataset.

* fix: activate dataset before recording observations and persist clearing account config

- seed-demo: call ActivateDataSet after RegisterDataSet to transition
  from DRAFT to ACTIVE before recording observations
- docker-compose: add DEPOSIT_CLEARING_ACCOUNT_ID env var passthrough
  so it persists across deployments
- .env.demo.example: document the clearing account config

* fix: register data source before recording market observations

RecordObservation requires a source_code identifying the data source.
Add RegisterDataSource call to create a SEED_DEMO source, and pass it
in each RecordObservationRequest. Extract price recording loop to
reduce cognitive complexity.

---------

Co-authored-by: Ben Coombs <bjcoombs@users.noreply.github.com>

Author: bjcoombs

cmd/seed-demo/main.go

@@ -482,15 +482,44 @@ func seedMarketData(ctx context.Context, conn *grpc.ClientConn) error {
 		return fmt.Errorf("activate dataset: %w", err)
 	}
 
-	// Seed 30 days of wholesale prices.
-	// UK wholesale prices vary between 15-35p/kWh with daily volatility.
+	// Register data source for seed observations
+	const sourceCode = "SEED_DEMO"
+	_, err = client.RegisterDataSource(ctx, &marketv1.RegisterDataSourceRequest{
+		Code:        sourceCode,
+		Name:        "Seed Demo Data Source",
+		Description: "Synthetic data generated by seed-demo for demonstration purposes",
+		TrustLevel:  80,
+	})
+	if err != nil {
+		if st, ok := status.FromError(err); ok && st.Code() == codes.AlreadyExists {
+			fmt.Println("  Data source SEED_DEMO already exists")
+		} else {
+			return fmt.Errorf("register data source: %w", err)
+		}
+	} else {
+		fmt.Println("  Registered data source: SEED_DEMO")
+	}
+
+	// Seed 30 days of wholesale prices
+	if err := recordWholesalePrices(ctx, client, sourceCode); err != nil {
+		return err
+	}
+
+	fmt.Println("  Recorded 30 days of wholesale energy prices")
+	fmt.Printf("  Fixed retail tariff: 24.5p/kWh\n")
+	fmt.Printf("  Wholesale range: ~15-27p/kWh (margin visible in account data)\n")
+
+	return nil
+}
+
+// recordWholesalePrices seeds 30 days of synthetic wholesale energy prices.
+func recordWholesalePrices(ctx context.Context, client marketv1.MarketInformationServiceClient, sourceCode string) error {
 	rng := rand.New(rand.NewSource(42)) //nolint:gosec
 	now := time.Now().UTC()
 	basePrice := 0.22 // 22p/kWh base wholesale price
 
 	for day := 30; day >= 1; day-- {
 		date := now.AddDate(0, 0, -day)
-		// Wholesale price with some trend and noise
 		dailyPrice := basePrice + (rng.Float64()-0.5)*0.10 // ±5p variation
 		if dailyPrice < 0.12 {
 			dailyPrice = 0.12 // floor
@@ -501,6 +530,7 @@ func seedMarketData(ctx context.Context, conn *grpc.ClientConn) error {
 
 		_, err := client.RecordObservation(ctx, &marketv1.RecordObservationRequest{
 			DatasetCode: "WHOLESALE_ENERGY_GBP_KWH",
+			SourceCode:  sourceCode,
 			ObservedAt:  timestamppb.New(startOfDay),
 			ValidFrom:   timestamppb.New(startOfDay),
 			ValidTo:     timestamppb.New(endOfDay),
@@ -515,10 +545,6 @@ func seedMarketData(ctx context.Context, conn *grpc.ClientConn) error {
 		}
 	}
 
-	fmt.Println("  Recorded 30 days of wholesale energy prices")
-	fmt.Printf("  Fixed retail tariff: 24.5p/kWh\n")
-	fmt.Printf("  Wholesale range: ~15-27p/kWh (margin visible in account data)\n")
-
 	return nil
 }