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/util/zlog/hostinfo.go

@@ -6,7 +6,7 @@ import (
 	"tailscale.com/tailcfg"
 )
 
-// SafeHostinfo wraps tailcfg.Hostinfo for safe logging.
+// SafeHostinfo wraps [tailcfg.Hostinfo] for safe logging.
 //
 // SECURITY: This wrapper intentionally redacts device fingerprinting data
 // that could be used to identify or track specific devices:
@@ -24,12 +24,12 @@ type SafeHostinfo struct {
 	hi *tailcfg.Hostinfo
 }
 
-// Hostinfo creates a SafeHostinfo wrapper for safe logging.
+// Hostinfo creates a [SafeHostinfo] wrapper for safe logging.
 func Hostinfo(hi *tailcfg.Hostinfo) SafeHostinfo {
 	return SafeHostinfo{hi: hi}
 }
 
-// MarshalZerologObject implements zerolog.LogObjectMarshaler.
+// MarshalZerologObject implements [zerolog.LogObjectMarshaler].
 func (s SafeHostinfo) MarshalZerologObject(e *zerolog.Event) {
 	if s.hi == nil {
 		return