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/versioncheck.go

@@ -84,7 +84,7 @@ func parseVersion(s string) (semver, error) {
 }
 
 // ensureDatabaseVersionTable creates the database_versions table if it
-// does not already exist. Uses GORM AutoMigrate to handle dialect
+// does not already exist. Uses [gorm.DB.AutoMigrate] to handle dialect
 // differences between SQLite (datetime) and PostgreSQL (timestamp).
 // This runs before gormigrate migrations.
 func ensureDatabaseVersionTable(db *gorm.DB) error {