Export mushaf layout data as JSON per page (#257)

[hammadxcm]

Description

Adds a JSON export format for mushaf layouts. Previously a layout could only be downloaded as SQLite (or DOCX); the JSON wiring existed but was commented out. This implements ExportMushafLayout#export_json and enables it in the download pipeline.

It writes one <page_number>.json file per page plus an info.json with mushaf metadata, into a dedicated json/ directory (so it doesn't collide with the DOCX pages/ output). The per-page logic reuses the exact same line/alignment helpers as the existing SQLite export (prepare_page_lines, get_line_alignment), so the two stay consistent.

Per-page structure:

{
  "page": 2,
  "lines": {
    "1": { "type": "surah_name", "alignment": "centered", "surah_number": 2 },
    "2": {
      "type": "ayah",
      "alignment": "justified",
      "first_word_id": 5,
      "last_word_id": 12,
      "data": ["ٱلٓمٓ", "ذَٰلِكَ", "ٱلۡكِتَٰبُ"]
    }
  }
}

info.json:

{ "name": "...", "number_of_pages": 604, "lines_per_page": 15, "font_name": "..." }

Word text for data is resolved via the layout's script using Mushaf#text_type_method — the same mechanism MushafLayoutJob already uses — so glyph-based mushafs (v1/v2) emit their glyph codes and text-based mushafs emit the appropriate script text.

Note: I kept the line type vocabulary (ayah / surah_name / basmallah) consistent with the existing SQLite export rather than the slightly different names sketched in the issue, so both downloads describe lines the same way. Happy to adjust the key names/structure if maintainers prefer.

Related Issue

Closes #257

Motivation and Context

The issue asks for per-page JSON so developers can integrate layout data directly without standing up a server to query the database. The export already supported SQLite/DOCX and had a commented-out JSON hook; this fills it in.

How Has This Been Tested?

• ruby -c passes on both changed files.
• RuboCop (Layout/Lint) reports no new offenses in the added code.
• The new export_page_json mirrors the already-in-production export_page (SQLite) logic line-for-line, and word-text resolution reuses the established word.send(mushaf.text_type_method) pattern from MushafLayoutJob.
• I was not able to run the exporter end-to-end against a seeded database in my environment, so a maintainer running export_mushaf_layouts for a sample layout to eyeball the generated JSON would be a valuable confirmation.

Screenshots (if appropriate):

N/A — backend export change.

[naveed-ahmad]

JAK