Bootstrap copied BFF and local accounts with public Sendico contracts (#34)

backend/contracts/sendico/models/ledger/balance.yaml

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+components:
+  schemas:
+    LedgerAccountBalance:
+      description: Canonical ledger account balance. Current and historical modes have distinct field-presence semantics.
+      oneOf:
+        - $ref: ./balance.yaml#/components/schemas/CurrentLedgerAccountBalance
+        - $ref: ./balance.yaml#/components/schemas/HistoricalLedgerAccountBalance
+
+    CurrentLedgerAccountBalance:
+      description: Current materialized ledger account balance.
+      type: object
+      additionalProperties: false
+      required:
+        - ledgerAccountRef
+        - balance
+        - version
+        - lastUpdated
+      properties:
+        ledgerAccountRef:
+          description: Ledger account reference.
+          $ref: ../objectid.yaml#/components/schemas/ObjectId
+        balance:
+          $ref: ../common/money.yaml#/components/schemas/Money
+        version:
+          description: Materialized account-balance version.
+          type: integer
+          format: int64
+        lastUpdated:
+          description: Materialized balance update timestamp.
+          type: string
+          format: date-time
+
+    HistoricalLedgerAccountBalance:
+      description: |
+        Event-time accounting balance reconstructed from posted statement-entry deltas
+        where `eventTime <= asOf`. This is not a materialized historical snapshot.
+      type: object
+      additionalProperties: false
+      required:
+        - ledgerAccountRef
+        - balance
+        - asOf
+      properties:
+        ledgerAccountRef:
+          description: Ledger account reference.
+          $ref: ../objectid.yaml#/components/schemas/ObjectId
+        balance:
+          $ref: ../common/money.yaml#/components/schemas/Money
+        asOf:
+          description: Canonical UTC RFC3339 event-time cutoff used for reconstruction.
+          type: string
+          format: date-time
+          example: '2026-04-23T12:30:00Z'

backend/contracts/sendico/models/ledger/operation.yaml

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+components:
+  schemas:
+    LedgerStatementVisibility:
+      description: Visibility of the account-history projection returned for the requested ledger account.
+      type: string
+      enum:
+        - full
+        - partial
+
+    LedgerEntryType:
+      description: Lowercase ledger entry type string from the BFF response.
+      type: string
+      example: transfer
+
+    LedgerLineType:
+      description: Lowercase posting-line type string from the BFF response.
+      type: string
+      example: main
+
+    LedgerAccountOperationSummary:
+      description: |
+        Account-history summary projection for a ledger statement entry.
+        `accountAmount` is the exact decimal sum of visible posting-line amounts whose `ledgerAccountRef`
+        equals the requested statement account. Positive means net credit, negative means net debit,
+        zero means net neutral, and the currency matches the requested ledger account currency.
+      type: object
+      additionalProperties: false
+      required:
+        - entryRef
+        - entryType
+        - accountAmount
+        - eventTime
+        - version
+        - visibility
+      properties:
+        entryRef:
+          description: Statement entry reference.
+          $ref: ../objectid.yaml#/components/schemas/ObjectId
+        entryType:
+          $ref: ./operation.yaml#/components/schemas/LedgerEntryType
+        accountAmount:
+          $ref: ../common/money.yaml#/components/schemas/Money
+        description:
+          description: Human-readable entry description when present.
+          type: string
+        eventTime:
+          description: Event timestamp carried by the canonical statement entry.
+          type: string
+          format: date-time
+        version:
+          description: Immutable ledger history version used for deterministic ordering.
+          type: integer
+          format: int64
+        visibility:
+          $ref: ./operation.yaml#/components/schemas/LedgerStatementVisibility
+
+    LedgerAccountOperationLine:
+      description: Visible posting line included in the account-history projection.
+      type: object
+      additionalProperties: false
+      required:
+        - ledgerAccountRef
+        - money
+        - lineType
+      properties:
+        ledgerAccountRef:
+          description: Ledger account reference for the visible posting line.
+          $ref: ../objectid.yaml#/components/schemas/ObjectId
+        money:
+          $ref: ../common/money.yaml#/components/schemas/Money
+        lineType:
+          $ref: ./operation.yaml#/components/schemas/LedgerLineType
+        organizationRef:
+          description: Owning organization reference when visible to the caller.
+          $ref: ../objectid.yaml#/components/schemas/ObjectId
+
+    LedgerAccountOperation:
+      description: |
+        Detailed account-history projection for a statement entry.
+        This payload is scoped to the requested ledger account and does not expose general journal-entry data outside that visibility model.
+      type: object
+      additionalProperties: false
+      required:
+        - entryRef
+        - entryType
+        - accountAmount
+        - eventTime
+        - version
+        - visibility
+        - lines
+      properties:
+        entryRef:
+          description: Statement entry reference.
+          $ref: ../objectid.yaml#/components/schemas/ObjectId
+        entryType:
+          $ref: ./operation.yaml#/components/schemas/LedgerEntryType
+        accountAmount:
+          $ref: ../common/money.yaml#/components/schemas/Money
+        description:
+          description: Human-readable entry description when present.
+          type: string
+        eventTime:
+          description: Event timestamp carried by the canonical statement entry.
+          type: string
+          format: date-time
+        version:
+          description: Immutable ledger history version used for deterministic ordering.
+          type: integer
+          format: int64
+        visibility:
+          $ref: ./operation.yaml#/components/schemas/LedgerStatementVisibility
+        lines:
+          description: Visible posting lines included in the account-history projection.
+          type: array
+          items:
+            $ref: ./operation.yaml#/components/schemas/LedgerAccountOperationLine
+        metadata:
+          description: Entry metadata when visible to the caller.
+          type: object
+          additionalProperties:
+            type: string
+        organizationRef:
+          description: Entry organization reference when visible to the caller.
+          $ref: ../objectid.yaml#/components/schemas/ObjectId