feat: complete EMF MVP — 100% byte-identical round-trip, full toolchain

[ronaldtse]

feat: complete EMF MVP — 100% byte-identical round-trip, full toolchain

Builds on PR #1. Drives the EMF corpus from 74% to 100% byte-identical
round-trip, completes the wire catalog, and lands the visitors, CLI,
docs, and CI workflows.

What lands

Wire layer correctness fixes (TODO 09 follow-up)

The biggest single win came from correcting layouts per MS-EMF 2.3.5:

• Rectangle/Ellipse/RoundRect: drop rclBounds — these only have
  rclBox (and szlCorner for RoundRect).
• Arc/ArcTo/Chord/Pie: drop rclBounds; layout is rclBox + ptlStart + ptlEnd.
• FillPath/StrokePath/StrokeAndFillPath: WithBounds (spec
  requires rclBounds).
• SelectClipPath: WithBounds + regionMode.
• Header: cbPixelFormat/offPixelFormat/bOpenGL/szlMicrometers
  are conditional on n_size, so 88/100/108-byte variants all parse.

Plus 57 missing wire types (full catalog at last):
SetPixelV, SetMetArgn, OffsetClipRgn, ExcludeClipRect, IntersectClipRect,
ExtSelectClipRgn, ScaleViewportExtEx, ScaleWindowExtEx, SetBrushOrgEx,
SetMapperFlags, RealizePalette, SelectPalette, CreatePalette,
ResizePalette, SetPaletteEntries, ExtFloodFill, FillRgn, FrameRgn,
InvertRgn, PaintRgn, BitBlt, StretchBlt, MaskBlt, PlgBlt,
SetDIBitsToDevice, AlphaBlend, TransparentBlt, SetLayout, SetIcmMode,
CreateMonoBrush, CreateDibPatternBrushPt, GradientFill, SmallTextOut,
DrawEscape, ExtEscape, NamedEscape, ColorCorrectPalette,
SetIcmProfileA/W, ForceUfiMapping, SetLinkedUfis, ColorMatchToTargetW,
CreateColorspaceW/Colorspace, SetColorspace, DeleteColorspace,
GlsRecord, GlsBoundedRecord, PolyTextOutA/W, PixelFormat,
SetTextJustification, PolyDraw/16, SetArcDirection, AngleArc.

Parser hardening (TODO 11 follow-up)

• Variable-array sanity check: rejects records whose declared point
  count exceeds nSize before bindata can hang on giant allocations.
  This was the cause of one emf-corrupted/ file timing out.
• Post-EOF trailing bytes captured on Metafile#trailing. Some
  writers append metadata after EMR_EOF; preserving it is necessary
  for byte-faithful round-trip.

TODO 16 — Round-trip harness

spec/emf/round_trip_spec.rb walks every non-corrupted fixture
(186 + 21 + 1 = 208 files) and asserts byte-identical
parse → serialize.

TODO 17 — Corrupted-resilience spec

spec/emf/corrupted_resilience_spec.rb walks the 21-file
emf-corrupted/ corpus with a 5-second timeout. Asserts each file
either parses (possibly with errors) or raises Emf::FormatError.

TODO 18 — Visitors

• Emf::Visitors::Stats — record-class histogram.
• Emf::Visitors::Dump — human-readable record-by-record dump.

Both override visit_emr_wire_record so the catch-all adapter produces
informative output.

TODO 19 — CLI

exe/emf now has real subcommands:

• version, help
• info FILE — header summary, record counts, device dims
• dump FILE — record-by-record dump
• validate FILE — exit 0 ok, 1 invalid
• stats FILE — record-type histogram
• round-trip FILE [--out PATH] — re-serialize, compare or write

spec/emf/cli_spec.rb exercises each via Open3.

TODO 20 — Documentation

• README.adoc — full rewrite with synopsis, CLI usage, architecture,
  constraints, roadmap.
• docs/architecture.adoc — three-layer design + MECE table.
• docs/format_notes.adoc — per-format quirks.
• CONTRIBUTING.adoc — branch policy, code style, how to add a record.
• CHANGELOG.adoc — Keep-a-Changelog format starting at 0.1.0.

TODO 21 — CI

• .github/workflows/test.yml — Ruby 3.1–3.4 × Ubuntu/macOS matrix.
• .github/workflows/release.yml — tag-triggered (v*) release to
  rubygems.org + GitHub release. Never runs on main commits.

Verification

• 321 specs, 0 failures (up from 75).
• Rubocop clean (182 files).
• bundle exec rake build produces pkg/emf-0.1.0.gem.
• Byte-identical round-trip on 100% of EMF fixtures: 186/186 in
  emf/, 21/21 in emf-ea/, 1/1 in simple/.
• All 21 emf-corrupted/ files parse without crashing or hanging.

What's still deferred

TODO	Title	Why deferred
10	Semantic per-record domain classes	WireAdapter works for now; emfsvg dispatches on type_id
11	2-pass path association (BEGINPATH ↔ FILLPATH/STROKEPATH)	emfsvg's rendering concern
07	WMF parser + fixtures	Next-format work; needs sourced fixtures
12–14	EMF+ structured parser	EMF+ payload is captured as raw bytes for now