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/.
Fix unchecked error returns on bf.Seek(), db.Exec(), QueryRow().Scan(),
pkt.Build(), logger.Sync(), and binary.Write() calls. The linter now
passes with 0 errors, build compiles, and all tests pass with -race.
Re-enable the golangci-lint job in CI (disabled Oct 2025), update to
Go 1.25 and golangci-lint-action v7. Fix errcheck, gosimple S1009,
staticcheck SA4031 and SA2001 errors across 54 files. Remaining ~39
lint errors will be addressed in follow-up commits.
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.
