all: apply godoc [Name] link conventions across comments

Every Go-identifier reference in // and /* */ comments now uses
godoc's [Name] linking syntax so pkg.go.dev and `go doc` render
them as clickable cross-references. No behaviour change.

Pattern applied across the tree:
  In-package         [Foo], [Foo.Bar]
  Cross-package      [pkg.Foo], [pkg.Foo.Bar]
  Stdlib             [netip.Prefix], [errors.Is], [context.Context]
  Tailscale          [tailcfg.MapResponse], [tailcfg.Node.CapMap],
                     [tailcfg.NodeAttrSuggestExitNode]

Skip rules:
  - File:line refs left as plain text
  - HuJSON wire keys inside backtick raw strings untouched
  - ACL/policy syntax tokens (tag:foo, autogroup:self, ...) not Go
    symbols, left as plain text
  - JSON/OIDC wire keys, gorm tags, RFC IPv6 placeholders, markdown
    link tags, decorative dividers — all left as-is

hscontrol/db/users.go

@@ -25,7 +25,7 @@ func (hsdb *HSDatabase) CreateUser(user types.User) (*types.User, error) {
 	})
 }
 
-// CreateUser creates a new User. Returns error if could not be created
+// CreateUser creates a new [types.User]. Returns error if could not be created
 // or another user already exists.
 func CreateUser(tx *gorm.DB, user types.User) (*types.User, error) {
 	err := util.ValidateUsername(user.Name)
@@ -47,7 +47,7 @@ func (hsdb *HSDatabase) DestroyUser(uid types.UserID) error {
 	})
 }
 
-// DestroyUser destroys a User. Returns error if the User does
+// DestroyUser destroys a [types.User]. Returns error if the [types.User] does
 // not exist or if there are user-owned nodes associated with it.
 // Tagged nodes have user_id = NULL so they do not block deletion.
 func DestroyUser(tx *gorm.DB, uid types.UserID) error {
@@ -92,8 +92,8 @@ func (hsdb *HSDatabase) RenameUser(uid types.UserID, newName string) error {
 
 var ErrCannotChangeOIDCUser = errors.New("cannot edit OIDC user")
 
-// RenameUser renames a User. Returns error if the User does
-// not exist or if another User exists with the new name.
+// RenameUser renames a [types.User]. Returns error if the [types.User] does
+// not exist or if another [types.User] exists with the new name.
 func RenameUser(tx *gorm.DB, uid types.UserID, newName string) error {
 	var err error