Add account trustlines metadata endpoint

[mayasimi]

resolve #9
summary
Implemented GET /account/:id/trustlines.

This returns all non-native balances for the account and enriches each trustline with issuer-provided asset metadata when available. For each asset, the endpoint loads the issuer account, reads home_domain, fetches https://<home_domain>/.well-known/stellar.toml, parses [[CURRENCIES]], and returns the matching asset’s name, description, and image.

A couple of implementation details worth calling out:

• Native XLM balances are excluded as requested.
• Issuer lookups and TOML fetches are cached per request to avoid duplicate work.
• Missing home_domain, unreachable TOML, parse failures, or missing currency metadata all resolve cleanly to toml: null.
• Account ID validation uses the existing validator.

Tests added for:

• Resolved TOML metadata
• Missing/unresolved issuer metadata
• Invalid account ID validation

Validation run:

• npm.cmd test -- --runInBand passes: 15/15

Note: lint could not be run because the repo is on ESLint 9 but does not currently include an eslint.config.* file.

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[Sulex45]

Resolve src/routes/account.js and tests/api.test.js before i can merge