feat: add Stellar bridge provider adapter interface

[Gyanee01]

Summary

Adds a provider-agnostic adapter contract for Stellar bridge integrations.

• Introduces normalized quote, route, execution, status, and error types.
• Defines the StellarBridgeProviderAdapter interface for bridge providers.
• Adds public exports for the Stellar adapter and quote type modules.
• Adds contract tests using a stub provider implementation.

Testing

• Added adapter contract test coverage for quotes, routes, execution, status checks, and error
  normalization.

Notes

• This establishes the integration boundary only; no concrete external bridge provider is implemented
  in this change.

[Copilot]

Pull request overview

Adds a provider-agnostic Stellar bridge adapter contract to establish a stable integration boundary for future bridge providers, along with canonical quote types and contract-level tests.

Changes:

• Introduces canonical StellarBridgeQuote (route/fees/execution/output) type definitions.
• Defines StellarBridgeProviderAdapter interface with normalized quote/route/execution/status/error contracts and exports it via adapter/interface barrels.
• Adds contract tests using a stub adapter implementation to validate the adapter surface and normalization expectations.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
tests/providers/stellar/stellar-bridge-provider-adapter.interface.spec.ts	Adds adapter contract tests using a stub provider implementation.
src/quotes/types/index.ts	Exports canonical quote types from the quotes/types barrel.
src/quotes/types/canonical-quote.ts	Defines canonical, provider-normalized Stellar bridge quote types.
src/providers/stellar/interfaces/stellar-bridge-provider-adapter.interface.ts	Introduces the Stellar bridge provider adapter contract types and interface.
src/providers/stellar/interfaces/index.ts	Re-exports the Stellar provider adapter interface from the interfaces barrel.
src/providers/stellar/index.ts	Updates Stellar provider barrel exports (currently contains merge-conflict markers).
src/providers/stellar/adapters/index.ts	Adds a public entry point for the adapter contract exports.

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