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/init_test.go

@@ -2,9 +2,9 @@ package zlog
 
 import "github.com/rs/zerolog"
 
-// init pins zerolog to TraceLevel for the zlog test binary.
+// init pins zerolog to [zerolog.TraceLevel] for the zlog test binary.
 //
-// zlog's tests use zerolog.New(&buf) and assert on Info-level output. zerolog's
+// zlog's tests use [zerolog.New] with a buffer and assert on Info-level output. zerolog's
 // (*Logger).should() gates emission on the global level, so any global level
 // above Info would silently break the assertions.
 //