Validate LightningConfig (sendable range, callback URL)

[Chemaclass]

Context

LightningConfig accepts values without validation. A misconfiguration (e.g. min > max sendable range, empty/invalid callback URL) surfaces late as confusing runtime behavior rather than a clear config-time error.

• src/Config/LightningConfig.php — fluent setters; setSendableRange(int $min, int $max), setCallbackUrl(string), setDomain(string).
• src/Shared/Value/SendableRange.php — withMinMax(int $min, int $max) does no ordering check.

Goal

Fail fast with clear messages on invalid configuration.

Scope / Tasks

• Validate the sendable range: min >= 1, max >= min (LUD-06: minSendable cannot be less than 1 or greater than maxSendable). Throw a clear exception otherwise — decide whether the guard lives in SendableRange::withMinMax() (preferred, single source of truth) or the setter.
• Validate callbackUrl is a non-empty, parseable URL (or documented base).
• Keep setDomain()'s scheme-stripping behavior; reject clearly empty/invalid domains.
• Unit tests for each invalid case (assert exception + message) and that valid configs are unaffected.

Implementation notes

• Prefer runtime validation with clear messages over silent coercion.
• Match existing exception style (RuntimeException with an interpolated, specific message), consistent with LightningConfig::addBackendsFile() and BackendType::fromString().
• Don't over-validate: only guard values that cause real downstream breakage.

Acceptance criteria

• min > max, min < 1, empty/invalid callback URL each throw a specific, actionable exception.
• Existing valid-config tests still pass.
• composer test-all green.

References

• LUD-06 min/maxSendable constraints: https://github.com/lnurl/luds/blob/luds/06.md