feat(stellar): SEP-0002 federation address resolver

[AJtheManager]

Implementation complete.

Added sdk/src/chains/stellar/federation.ts (~300 lines) implementing SEP-0002 federation resolution:

• resolveStellarFederation(input, options?) — splits name*domain.tld, fetches https:///.well-known/stellar.toml (SEP-0001), extracts FEDERATION_SERVER, queries it, validates account_id with StrKey, returns { accountId, stellarAddress, memo?, resolvedAt }. Pass-through for valid G… / M… inputs.
• In-memory cache keyed by federation address with a configurable TTL (default 1h). clearFederationCache, setFederationDefaultTtl, getFederationDefaultTtl exposed.
• FederationResolutionError with discriminated code: INVALID_ADDRESS, TOML_FETCH_FAILED, FEDERATION_SERVER_MISSING, FEDERATION_SERVER_FAILED, INVALID_RESPONSE, TIMEOUT, INSECURE_PROTOCOL.
• AbortController-based timeout (default 10s). HTTPS enforced unless allowInsecureHttp: true. Injectable fetchImpl for tests/proxies.

Tests sdk/test/chains/stellar/federation.test.ts:

• 19 unit tests with mocked fetch covering happy path, memo handling, cache hit/miss/TTL expiry/noCache/cacheTtlMs: 0, G-address passthrough, every error code, timeout via signal abort, and the error class itself. All pass.
• Opt-in integration test gated on FEDERATION_INTEGRATION=1 + FEDERATION_ADDRESS= (optional FEDERATION_EXPECTED_ACCOUNT). Skipped by default — same pattern used by multisig.integration.test.ts / swap.integration.test.ts.

closes #78

[truthixify]

Conflict on pnpm-lock.yaml after #110 (TypeDoc) just landed. Quick rebase:

git fetch origin
git rebase origin/develop
pnpm install
git add pnpm-lock.yaml
git rebase --continue
git push --force-with-lease

Federation code itself looks clean — just the lockfile.