feat: reading time in the byline, through a Block Bindings source

[ogorzalka]

Pollora roadmap 2.4, step 4b: Buzz shows the framework's Block Bindings.

• app/Cms/Bindings/ArticleBinding.php: #[BlockBinding('%theme_name%/article')] with reading_time (230 words a minute, at least 1) and word_count, computed from the post's words.
• patterns/article.php and patterns/index-list.php: the byline gains · 4 min read, a core/paragraph bound to reading_time (per post in the query loop).
• E2E: a 700-word post reads "4 min read" on its page and in the index, a short one "1 min read".
• README: where the source lives and how to add a field.

Buzz has no typed meta of its own, so a computed source is the binding that makes sense without content setup. Requires framework ≥ v13.34.6 (Block Bindings), which the locked skeleton already installs.

Checked on a local Buzz site (framework develop): front, index loop (per-post values), editor preview endpoint, pollora:binding:list, pollora:doctor ("2 block binding(s), each able to show its value"), and the full Buzz E2E spec (12/12, Chromium).