docs: add doc.go files and godoc comments to all packages

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/.

common/gametime/doc.go

@@ -0,0 +1,4 @@
+// Package gametime provides time helpers anchored to the JST (UTC+9) timezone
+// used by Monster Hunter Frontier's game clock, including weekly reset
+// boundaries and the in-game absolute time cycle.
+package gametime

common/gametime/gametime.go

@@ -4,16 +4,19 @@ import (
 	"time"
 )
 
+// Adjusted returns the current time in JST (UTC+9), the timezone used by MHF.
 func Adjusted() time.Time {
 	baseTime := time.Now().In(time.FixedZone("UTC+9", 9*60*60))
 	return time.Date(baseTime.Year(), baseTime.Month(), baseTime.Day(), baseTime.Hour(), baseTime.Minute(), baseTime.Second(), baseTime.Nanosecond(), baseTime.Location())
 }
 
+// Midnight returns today's midnight (00:00) in JST.
 func Midnight() time.Time {
 	baseTime := time.Now().In(time.FixedZone("UTC+9", 9*60*60))
 	return time.Date(baseTime.Year(), baseTime.Month(), baseTime.Day(), 0, 0, 0, 0, baseTime.Location())
 }
 
+// WeekStart returns the most recent Monday at midnight in JST.
 func WeekStart() time.Time {
 	midnight := Midnight()
 	offset := int(midnight.Weekday()) - int(time.Monday)
@@ -23,10 +26,13 @@ func WeekStart() time.Time {
 	return midnight.Add(-time.Duration(offset) * 24 * time.Hour)
 }
 
+// WeekNext returns the next Monday at midnight in JST.
 func WeekNext() time.Time {
 	return WeekStart().Add(time.Hour * 24 * 7)
 }
 
+// GameAbsolute returns the current position within the 5760-second (96-minute)
+// in-game day/night cycle, offset by 2160 seconds.
 func GameAbsolute() uint32 {
 	return uint32((Adjusted().Unix() - 2160) % 5760)
 }