Alliance applications were hardcoded to always-open. Add a `recruiting`
column to guild_alliances and handle OperateJoint actions 0x06 (Allow)
and 0x07 (Deny) confirmed via Wii U debug symbols. Only the parent
guild leader can toggle the setting, matching the existing disband guard.
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/.
