Document ProxyEntity opcode workflow

[konard]

Summary

Adds a Markdown explanation of the current ACAD_PROXY_ENTITY implementation under cad_source/zcad/velec/uzeentproxy/.

The document covers:

• how DXF 310 proxy graphic chunks are collected into FProxyDataBytes;
• the binary Proxy Graphic command layout and command boundary handling;
• system OpCode handling for state, fill, lineweight, linetype, true color, and matrix stack;
• registration and dispatch through TProxyOpCodeDispatcher;
• supported geometric OpCodes and their parser modules;
• how parsed primitives become TProxyContour / TProxyTextItem instead of native ZCAD entities;
• what rendering primitives are actually used: Representation.DrawPolyLineWithLT, uzeTriangulator, Representation.DrawTextContent, and final Representation.DrawGeometry;
• current limitations and the relevant file map.

Testing

Documentation-only change. No runtime tests were required.

Issue

Closes #926

[konard]

🤖 Solution Draft Log

This log file contains the complete execution trace of the AI solution draft process.

💰 Cost estimation:

• Model: gpt-5.4
• Provider: OpenAI
• Public pricing estimate: unknown
• Token usage: 94,115 input, 7,534 output, 1,222,784 cache read, 0 cache write

📊 Context and tokens usage:

Total: (94.1K + 1.2M cached) input tokens, 7.5K output tokens

🤖 Models used:

• Tool: OpenAI Codex
• Requested: gpt-5.4
• Model: GPT-5.4 (gpt-5.4)

📎 Log file uploaded as Gist (13845KB)

• View complete solution draft log

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Now working session is ended, feel free to review and add any feedback on the solution draft.

[konard]

✅ Ready to merge

This pull request is now ready to be merged:

• CI workflows exist but were not triggered for this commit
• No merge conflicts
• No pending changes

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