refactor(text): render the annotated display view client-side

[HugoFara]

Stack 5 of 6. Base: #301 (needs ConfigIsland). Two commits: the endpoint
fix, then the conversion that depends on it.

/text/{id}/display was the last page still building content in PHP — it parsed
the stored annotation and echoed a <ruby> per term. It now ships a shell and
fetches GET /api/v1/texts/{id}/annotation, the endpoint the print view already
used, so display_main.php, display_header.php and display_text.php
collapse into one display_alpine.php.

First commit: two gaps in the endpoint

• Items carried no romanization, so a client could only get one by querying
  per word. Added, resolved for the whole text in a single query — the
  annotated view renders every word at once, so the naive form would be hundreds
  of round trips on a normal text.
• Blank rows came back as words with empty text. Splitting the stored
  annotation on newlines yields an entry for any trailing or repeated newline,
  and the endpoint reported those as terms. The annotated print view has been
  rendering two empty <ruby> elements per text as a result — a pre-existing
  bug, not one introduced here. They are now skipped, matching the rule
  TextDisplayService::parseAnnotationItem() has always applied.

Second commit: the conversion

The generated markup is deliberately identical to what PHP emitted —
.anntermruby for the term inside <rb>, .anntransruby2 for the translation
inside <rt>, romanization as a title attribute, and a paragraph marker
closing and reopening <p> at the language's text size with the same 1.35 then
1.3 line heights. annotation_toggle.ts drives the show/hide buttons by
querying those classes at click time, so anything else would break them
silently.

Prev/next navigation stays server-rendered. It reads the request's language
filter, search query and tag selection out of the session, none of which has an
endpoint, and it is chrome rather than content.

Verified against real data, not just tests

Both annotated texts in a live database, before and after: same paragraph count,
same term count (77 and 42), same line heights, zero empty rubies, toggles still
masking the right elements. The item counts now match
TextDisplayService::parseAnnotations() exactly, which is the old renderer's
own parser.

Stack: #298 → #299 → #300 → #301 → 5 → #6