Render tracked changes and comments

[ikashapov]

Render tracked changes and comments

Closes #154. Three commits, each one revision-layer capability:

1. w:strike / w:dstrike actually draw (b78f729)

§17.3.2.37/§17.3.2.9 were parsed and style-cascaded, then silently dropped at
the RunProperties→FontProps seam — struck text painted plain (sample1's own
body literally says "underlined and struck out text", rendered un-struck).
The underline path was the template: strike metrics come from Skia's
strikeout values (positive above the baseline, 0.3×ascent fallback), filled
by the same decoration pass, emitted as DrawCommand::Line — two straddling
lines for dstrike — in the run's color. Zero painter changes: Line and
Underline already share an arm. Groundwork for the deletion marks below.

2. Tracked-change marks per the document's own view (afca99f)

The parse kept a hard-coded "accept all changes" view: <w:ins> flattened to
plain text, <w:del> dropped with its content. Both wrappers now flatten
with their runs stamped (TextRun.revision — kind + author), and the
display decision moves to the renderer, keyed on w:settings/w:revisionView:

• Markup view (the default): deletions struck through, insertions
  underlined, each in a per-author color assigned by first appearance in
  document order (resolve::revision — the palette is engine-defined; Word's
  is user-configurable).
• Final view (revisionView hides insDel): deleted runs filtered out
  beside the w:vanish filter; insertions plain.

Deleted pictures cannot carry a run stamp and stay dropped in every view —
exactly the pre-change behavior, now scoped to what a run cannot express.
Nested wrappers shadow (inserted-then-deleted is a deletion); moveFrom
stays dropped so moved text isn't duplicated, moveTo renders plain.

3. Comments: range wash, margin balloons, connectors (650daf1)

word/comments.xml (§11.3.1) parses through the notes-part machinery with
author/initials kept. Three things reach the page when the view shows
comments:

• Range wash — commentRangeStart/End (paragraph and block level)
  toggle a parse-time stamp on the runs between them, so a range survives
  paragraph boundaries; stamped runs get a pale wash. Word's print view
  brackets the range instead — the wash is a documented engine choice.
• Anchors — each w:commentReference becomes a zero-width fragment
  (the bookmark pattern) resolved to a page position at line emission.
• Balloons — a post-layout pass (shaped like the header/footer second
  pass) consumes each page's anchors and draws into the right margin band:
  author label and body in the author's palette color (comment authors join
  the tracked-change palette, so one person keeps one color across both),
  border, background, connector line from the anchor, later balloons
  stacking below earlier ones. A margin too narrow for readable text (< 24pt
  of band) draws nothing, with a warning — Word widens the sheet for its
  markup area, which a fixed page cannot.

w:revisionView w:comments="0" suppresses all three.

Adversarial review round

A four-dimension adversarial review (parse-state leaks, view semantics,
balloon geometry, docs/test honesty) confirmed 21 findings; all are fixed in
the review commit (d595617):

• w:delInstrText — Word's spelling of a deleted complex field — was a hard
  parse error failing the whole document; it now parses.
• The deleted-content filter is an explicit retain-list: a deleted symbol,
  note reference, dynamic field, or mc:AlternateContent-wrapped shape can
  no longer leak into either view (a deleted DATE field used to re-evaluate
  and paint a fresh value in the final view).
• Deletion is sticky across nesting (<w:ins> inside <w:del> stays
  deleted); a wholly deleted paragraph (§17.13.5.15 mark deletion, now
  modelled) merges away in the final view instead of leaving a blank line.
• Comment ranges: table- and row-level markers now toggle the stamp in
  document order; a commentReference closes its own range (the repair for
  a lost end marker); orphaned range ids wash nothing; notes get a fresh
  conversion context each so an unbalanced marker cannot leak across notes.
• Balloons: one balloon per comment document-wide (repeated w:tblHeader
  rows no longer duplicate it), the endnote page gets its own balloon pass,
  page-bottom overflow and tables-in-comments are warned about.
• Docs: the README Strikethrough row flips to ✅ (77 ✅ / 11 ⚠️ / 10 ❌), the
  per-author-colors and row-deletion scope lines are stated, and three stale
  schema/module doc claims are corrected.

Verification

• Full battery green: fmt, clippy -D warnings, 46 test suites, doc,
  --no-default-features.
• Corpus pixel-diff against the base commit shows exactly three diffs,
  each explained: the comment-reference.docx comment now renders (the
  feature), and the struck runs of sample1 / numbering-direct-indent
  now paint struck (the strike fix).
• New fixtures, all generator-built, OPC-verified, and paired with a
  view-flipped twin: tracked-changes.docx / -final.docx (the strike
  paragraph in both is the discriminator between a revision mark and strike
  formatting), comments.docx / comments-hidden.docx (two authors, a
  multi-paragraph balloon, a cross-paragraph range). The Word-authored
  corpus fixture comment-reference.docx (Cyrillic author, narrow margin,
  modern-comments sibling parts) is exercised end-to-end.
• Mutation checks on the strike emission and metrics sign, the revision
  overlay and final-view suppression, the wash, the range stamp, and the
  balloon pass — every deliberate break was caught by exactly the tests
  written for it.
• Rendering verified visually against LibreOffice for both fixture families.

README coverage rows flip to ✅ (77 ✅ / 11 ⚠️ / 10 ❌; FAQ gap list drops
"tracked changes and comments"); AGENTS.md corpus table documents the new
fixtures and the now-rendering comment fixture.