Auto-tag Apply tags headings by size and weight (#7062) (#7069)

* feat(a11y): auto-tag Apply tags headings by size and weight

Apply now chooses H1-H6 or P per text object instead of P for all.
The body style is the half-point size showing the most characters (bold
when most of those are bold). A short object (at most 3 lines, 200
characters, with a letter) is a heading when it is 1.15x the body, or
bold at 0.9x the body over a regular body in at most 2 lines. Heading
styles rank across the document, larger and bolder first, capped at H6,
and a level never skips past the one before it so heading-nesting
passes.

Size is Tf x Tm x CTM with q/Q tracked; bold is Metrics.bold. Text in
render mode 3 (an OCR layer) is not counted. Font metrics are measured
once per font object per document, at most 256 fonts.
AutoTagResult gains a headings count. Parity, gaps, roadmap and the
apply tool's note say headings are tagged.

Fixes #7062.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* fix(a11y): rank heading styles by map and skip clip-only text

Look up each heading style's rank in a map built once after sorting,
so ranking is linear in the number of text objects. Text in render
mode 7 (clip only) paints nothing, so it is excluded from heading
evidence like mode 3.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

---------

Co-authored-by: KenM76 <KenM76>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

parity/acrobat-features.toml

@@ -9158,8 +9158,8 @@ milestone = "M12"
 status = "partial"
 commands = ["a11y.autotag"]
 tools = ["accessibility_autotag_preview", "accessibility_autotag_apply"]
-evidence = ["crates/automation/tests/it/automation.rs::autotag_preview_proposes_text_without_changing_the_pdf", "crates/automation/tests/it/automation.rs::autotag_apply_writes_reviewable_tags_and_survives_save_reopen", "crates/ui-egui/tests/it/accessibility.rs::automatic_text_tagging_opens_reviewable_tags"]
-notes = "Auto-tag writes real marked content, a Document structure element, P tags and a parent tree for text-only PDFs, with undo and Tags-panel review. It refuses mixed content, forms, annotations and existing tags. The preview separately proposes headings. Images, tables, lists, links, fields and headings are not classified or tagged by Apply."
+evidence = ["crates/automation/tests/it/automation.rs::autotag_preview_proposes_text_without_changing_the_pdf", "crates/automation/tests/it/automation.rs::autotag_apply_writes_reviewable_tags_and_survives_save_reopen", "crates/automation/tests/it/automation.rs::autotag_apply_tags_headings_by_size_across_pages", "crates/a11y/src/autotag_roles.rs::levels_rank_styles_largest_first_and_never_skip_a_level", "crates/ui-egui/tests/it/accessibility.rs::automatic_text_tagging_opens_reviewable_tags"]
+notes = "Auto-tag writes real marked content, a Document structure element, H1-H6 and P tags and a parent tree for text-only PDFs, with undo and Tags-panel review. A text object is a heading when it is short and larger or bolder than the body text; levels rank those styles across the document and never skip a level. It refuses mixed content, forms, annotations and existing tags. The preview still proposes headings by its own single-line rule, so it can differ from Apply. Running headers and footers can still become headings (#7065); invisible text (render mode 3) is ignored. Images, tables, lists, links and fields are not classified or tagged by Apply."
 
 [[feature]]
 id = "a11y.autotag-fields"