Add support for legacy AutoCAD R14 ASCII DWF

[brownie-cake]

Root cause

The customer drawing is a pre-DWF-6 readable WHIP!/W2D stream (DWF V00.34) produced by AutoCAD R14, not a ZIP-based DWF 6+ package. The loader correctly recognized it as text, but the existing textual fallback was line-oriented and only understood fixture-style commands. It therefore could not parse real compact WHIP opcodes or counted point sets that continue across physical lines.

Fix

• Add a bounded, linear-time stream scanner for legacy readable DWF.
• Parse the core C, L, P, T, M, F/f, and V/v opcodes.
• Parse palette colors, source background, line weight, marker size, and extended ASCII operands.
• Triangulate T polytriangle strips with alternating winding and degenerate-strip handling.
• Distinguish filled P polygons from unfilled polylines.
• Preserve the declared DWF background across Canvas, WASM, and WebGL by emitting a page-sized backdrop primitive.
• Classify successfully parsed readable streams as classic dwf documents rather than unknown text.

Regression coverage

The proprietary Mercedes-Benz drawing remains local and is not committed. A synthetic DWF V00.34 fixture covers multiline point sets, palette/background handling, triangle strips, fill state, markers, visibility, and hidden URL geometry.

Production validation asserts:

• exactly 8 fixture primitives;
• polyline: 3, polygon: 3, rect: 2;
• black source backdrop;
• zero non-info diagnostics.

Customer-file verification

• document kind: dwf;
• page kind: w2d-text;
• 19,572 renderable primitives including the source backdrop;
• 0 warning/error diagnostics;
• complete Mercedes electrical diagram visually restored in the raster preview;
• parse time approximately 40 ms on the local Node validation run.

Local checks

• isolated strict TypeScript parser compile: passed;
• loader/parser integration compile: passed;
• customer-file parse and visual render inspection: passed;
• synthetic fixture assertions: passed.

[brownie-cake]

Final verification complete.

• CI run 13: passed (build, validate:production, check:examples, build:demo, pack:dry).
• Cloudflare Pages demo run 13: demo build and artifact upload passed; deployment was intentionally skipped for the pull-request context.
• Customer Mercedes-Benz DWF: opened as dwf / w2d-text, produced 19,572 renderable primitives including the black source backdrop, and reported zero warning/error diagnostics.
• The customer drawing was not committed; only the synthetic legacy DWF V00.34 regression fixture is public.
• PR is conflict-free and mergeable.