feat: Rewrite seed-demo to use ApplyManifest for structural provisioning (#1693)

* feat: Rewrite seed-demo to use ApplyManifest for structural provisioning

Add volterra-energy-demo.json manifest containing all structural resources:
instruments (GBP, KWH, CARBON_CREDIT), account types (ENERGY_TRADING,
INVENTORY_KWH, CARBON_INVENTORY, SETTLEMENT), market data source (SEED_DEMO)
and dataset (WHOLESALE_ENERGY_GBP_KWH), valuation rules, organizations (UK
Power Networks DNO + 4 Grid Supply Points), and GSP KWH inventory internal
accounts.

Replace direct RegisterInstrument, CreateDraft/ActivateAccountType,
RegisterDataSource/RegisterDataSet, and createGSPInternalAccounts calls in
seed-demo with a single ApplyManifest call. Idempotent reapply returns
NO_CHANGE for structural resources.

Keep operational seeding via direct gRPC: customer party registration,
current account creation, balance deposits, and price observations remain
runtime data outside the manifest.

After manifest apply, GSP internal account IDs are resolved by account code
and the DNO party ID is resolved by external reference, replacing the
previous approach of creating these resources imperatively.

* fix: Address CodeRabbit review feedback on seed-demo manifest rewrite

- Add pagination loop to resolveOrganizationPartyID to avoid false
  not-found errors in tenants with more than 100 parties
- Add CARBON_MARKET dataset to volterra-energy-demo.json so the
  CARBON_CREDIT→GBP valuation rule references a declared data source
  rather than an undefined code

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

Author: bjcoombs