Add DEBUG logging to broadcast path, use parent logger in embedded mode

[shruggr]

Summary

• Add DEBUG-level logging throughout the broadcast submission path in the embedded service: transaction entry, per-endpoint response with timing, broadcast completion, and WARN for timeouts and unexpected status codes
• Add DEBUG-level logging to the teranode HTTP client for request/response
• Initialize() now uses the parent logger when provided instead of creating its own, enabling per-module log level control from the host application (e.g., 1sat-stack's NewComponentLogger with level override). Falls back to config-based logger for standalone mode.

Why

When debugging broadcast failures (transactions stuck in RECEIVED status, invalid merkle paths, etc.), there was zero visibility into what happened during the submission flow. These logs are all DEBUG level so they don't impact production — operators set arcade.log_level: debug only when diagnosing issues.

The logger passthrough fixes a disconnect where the host application configured a debug-level logger for the arcade component, but Initialize() discarded it and created its own INFO-level logger.

Test plan

• go build ./... passes
• Verify DEBUG logs appear when arcade log level is set to debug in the host application
• Verify no log output at INFO level (default) from the new log lines