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

integration/dsic/dsic.go

@@ -136,7 +136,7 @@ func (dsic *DERPServerInContainer) buildEntrypoint(derperArgs string) []string {
 	return []string{"/bin/sh", "-c", strings.Join(commands, " ; ")}
 }
 
-// New returns a new TailscaleInContainer instance.
+// New returns a new [tsic.TailscaleInContainer] instance.
 func New(
 	pool *dockertest.Pool,
 	version string,
@@ -179,7 +179,7 @@ func New(
 	}
 
 	// Install the CA cert so the DERP server trusts its own certificate
-	// and any headscale CA certs passed via WithCACert.
+	// and any headscale CA certs passed via [WithCACert].
 	dsic.caCerts = append(dsic.caCerts, tlsCACert)
 
 	for _, opt := range opts {
@@ -319,7 +319,7 @@ func (t *DERPServerInContainer) Version() string {
 	return t.version
 }
 
-// ID returns the Docker container ID of the DERPServerInContainer
+// ID returns the Docker container ID of the [DERPServerInContainer]
 // instance.
 func (t *DERPServerInContainer) ID() string {
 	return t.container.Container.ID