feat: add API Service starter template

[dDevAhmed]

Summary

Implements CLI-030 by adding the trusted MVP api-service starter as a dependency-light Node.js backend with an explicit Stellar integration boundary.

This PR is temporarily stacked on CLI-029 so its diff remains isolated while PR #75 completes repository gates. After CLI-029 lands, this can target main directly.

Included

• bundled api-service template wired into controlled template resolution
• Node.js ESM service with no runtime dependencies
• GET /health service health route
• GET /stellar/network public network configuration route
• validated API port and Stellar endpoint configuration
• HTTPS enforcement for non-local Stellar endpoints
• isolated src/stellar-client.js boundary with no fabricated SDK/network calls
• .env.example using Testnet public endpoints only
• .gitignore protecting local .env
• generated README covering start, environment, test, and safe Stellar extension guidance
• template-local tests using an ephemeral localhost port
• CLI-level smoke test that generates the project and runs its check and test scripts

Security

• no seed phrases, signing keys, credentials, or private-key fields
• no remote template loading or arbitrary path loading
• no outbound Stellar calls in generated tests
• remote endpoint configuration rejects plain HTTP
• SDK/signing functionality is intentionally not fabricated and remains behind a documented integration boundary

Closes #33