Add acodepng-based PNG generator tab to UI sender

[peterwolf-pl]

Motivation

• Add a separate PNG->ACODE generator flow driven by acodepng.py without changing the existing artacodepng pipeline.
• Expose acodepng.py-specific options in the web UI so users can tune generation parameters matching the script's CLI.
• Provide preview and simulator wiring for the new generator consistent with other generator tabs.

Description

• Introduced ACODEPNG_PATH and updated _assert_tools_exist to accept a list of script paths, and adjusted existing checks to pass explicit tool lists.
• Implemented generate_from_acodepng(png_path, params) and a new Flask endpoint @app.route("/api/gen_acodepng", methods=["POST"]) to run acodepng.py and generate preview via acodeviz.py.
• Added a new UI tab Generator PNG (acodepng) in templates/index.html with settings (prefix ap_), client-side JS (generateAcodepng, lastAcodepngId) and simulator instance simAcodepng, including push/download wiring to the sender.
• Kept the existing artacodepng generator intact and mirrored simulator behavior and preview generation to match other generator tabs.

Testing

• Ran python3 acodepng.py --help to inspect available CLI options, which executed successfully and was used to map UI fields to CLI flags.
• Attempted to start the UI with python3 ui_sender.py, which failed to run due to missing flask module (automated start failed).
• No additional automated unit tests were added or executed as part of this change.
• Basic repository operations (git commit) were performed to record the changes.

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