refactor: Remove unused code and fix nil dereference issues
- Remove unused exported functions from pkg/database (session tracking,
bulk hashrate inserts, various query helpers)
- Remove unused exported functions from pkg/node (identity management,
bundle operations, controller methods)
- Make internal-only functions unexported in config_manager.go and database.go
- Remove unused EventProfile* constants from events.go
- Add GetCommit() and GetBuildDate() to expose version.go variables
- Fix potential nil dereference issues flagged by Qodana:
- Add nil checks for GetIdentity() in controller.go, transport.go, worker.go
- Add nil checks for GetPeer() in peer_test.go
- Add nil checks in worker_test.go
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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