Switch VK Ads landing to FastAPI

[gistrec]

Summary

• migrate the VK Ads landing endpoint to FastAPI with inline HTML rendering and uvicorn startup
• shorten VK Ads tokens to 32-character hex strings and update the schema and docs accordingly
• refresh dependencies and docs for the FastAPI-based landing server

Testing

• not run (not requested)

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Codex Task

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Avoid double-encoding VK Ads goal parameter

The Mail.ru tracker call is built with e=f"RG%3A0/{goal}", but httpx URL-encodes params again, so the request goes out as e=RG%253A0%2FstartBot (verified with httpx.Request(...).url), not the documented e=RG%3A0/startBot shown in README. That double-encoding means every VK Ads start payload sends an unrecognized goal value, so conversion tracking is likely dropped.

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