Add package-level documentation (doc.go) to all 22 first-party
packages and godoc comments to ~150 previously undocumented
exported symbols across common/, network/, and server/.
Add explicit error discards (_ =) for Close() calls on network
connections, SQL rows, and file handles across 28 files. Also add
.golangci.yml with standard linter defaults to match CI configuration.
Wrap *rand.Rand in a mutex-protected SafeRand type to make the global
RNG safe for concurrent use across goroutines. The previous bare
*rand.Rand caused data races detected by go test -race.
