Navigable section anchors: slug ids + self-links on h1/h2, scroll-tracked location hash.

Long-enough articles (3+ in-body h1/h2) get slug ids (python-slugify,
mirroring the editor's slugify.js) and the heading text becomes a
self-link (a.anchor) for clean link copying; {#id} always wins,
duplicates get -2/-3 suffixes, h3+ never. The implicit page title is
now injected as '# {title}' into the markdown (render(title=...)), so
it takes the same first-h1 path as an explicit one: no id, href=""
self-link scrolling to top, not counted toward the threshold. The
.body wrapper is gone — segments are direct article children — and the
editor preview swaps the whole article in one go. pagerite.js tracks
the reading position in the location hash (last tagged heading above
the viewport middle; cleared at the top, never on unscrollable pages)
and scrolls to anchors after fetch-navigation.

AGENTS.md

@@ -46,7 +46,7 @@ Server run by CLI entry point `uv run pagerite` (no auto reloads, build needed).
     - Maintaining and owning the app's own `Data` object is preferable; Kanta never copies this, only edits in place
     - Note: besides opening it every access is immediate direct variable access: no `await`, no locks, no delays
   - **fastapi-vue** — template glue for serving/building the Vue frontend; keep its integration points (`Frontend`, build hook) intact.
-  - **markdown-it-py** — Markdown rendering with `html=True` raw passthrough; mdit-py-plugins for footnote/deflist/tasklists/attrs; **Pygments** for server-side code highlighting (`nowrap` spans, styled by `frontend/src/assets/pygments.css` which maps token classes 1:1 onto the `--code-*` variables; light/dark palette sets live in `pagerite.css` and resolve via `light-dark()` from the theme's `color-scheme` — themes pick a set, not individual colors).
+  - **markdown-it-py** — Markdown rendering with `html=True` raw passthrough; mdit-py-plugins for footnote/deflist/tasklists/attrs; in-body h1/h2 headings get auto slug ids + self-links when the body has 3+ of them (`python-slugify`, mirroring `slugify.js`); **Pygments** for server-side code highlighting (`nowrap` spans, styled by `frontend/src/assets/pygments.css` which maps token classes 1:1 onto the `--code-*` variables; light/dark palette sets live in `pagerite.css` and resolve via `light-dark()` from the theme's `color-scheme` — themes pick a set, not individual colors).
 
 ## Conventions