Add TOC plugin for server-side table of contents generation

[rolfedh]

Summary

• Fixes Create a TOC plugin #579
• Adds a new roq-plugin-toc module that generates a table of contents from page headings in Markdown and AsciiDoc content
• The plugin is a standalone opt-in dependency (not bundled in the quarkus-roq aggregate extension)

How it works

The plugin parses rendered page HTML with JSoup, extracts headings (h1–h6) that have id attributes, and builds a nested hierarchy. It exposes two Qute template extensions on Page:

• {page.toc} — returns a List<TocEntry> with id, title, level, and children properties for custom rendering
• {page.tocHtml} — returns a pre-rendered <nav class="roq-toc"> HTML block with nested <ul> lists and anchor links

Both AsciiDoc (div.sect* sections) and Markdown (h*[id] elements) heading formats are supported. All HTML output is XSS-escaped.

This implementation generates static HTML on the server side, consistent with the issue request to "generate the TOC dom in the content." JavaScript-based scroll tracking or active-section highlighting would be a follow-up enhancement.

What's included

• roq-plugin/toc/ — new plugin module (deployment + runtime)
• 16 unit tests covering heading extraction (Markdown + AsciiDoc), hierarchy building, HTML rendering, and XSS escaping
• AsciiDoc documentation page with concept, how-to, and reference sections
• Navigation and index updates

LLM disclosure

This PR was developed with assistance from Claude Code (Claude Opus 4.6). All code was reviewed, tested, and verified by the author.

Test plan

• mvn install -DskipTests — full project build succeeds
• mvn test -pl roq-plugin/toc/runtime — 16 unit tests pass
• mvn verify — no cross-module regressions (pre-existing RoqCodestartTest failures unrelated)
• Manually tested with blog/ example: TOC renders correctly for both Markdown and AsciiDoc posts

[ia3andy]

Thanks for the contribution ! I am busy this week, I'll have a careful look next week!