docs: add Table of Contents to README

README has 15 H2 sections and no navigational aid before this point.
Anchors verified mechanically against actual headings (15/15 match, 0 broken).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GiiyJydBvq1qPbHB4Qg8Mz

README.md

@@ -6,6 +6,24 @@ Playgrounds are the visual self-service UIs that complement a plugin's terminal
 
 **Version:** 0.6.0 — see [CHANGELOG.md](CHANGELOG.md).
 
+## Table of Contents
+
+- [Non-goals](#non-goals)
+- [Provenance](#provenance)
+- [Directory layout](#directory-layout)
+- [Quick start](#quick-start)
+- [Design principles](#design-principles)
+- [Token system](#token-system)
+- [Component reference](#component-reference)
+- [Schemas](#schemas)
+- [Theming](#theming)
+- [Print mode](#print-mode)
+- [Known limitations](#known-limitations)
+- [Self-hosted fonts](#self-hosted-fonts)
+- [Versioning](#versioning)
+- [License](#license)
+- [Contributing](#contributing)
+
 ## Non-goals
 
 - **Not a JavaScript component library.** The system is CSS-only. Interactivity (tab state, sidepanel toggling, live-meter updates) is wired by each Playground in vanilla JS.