New backend/technical_check.py extracts technical metadata from
uploaded assets via PIL (images), PyMuPDF (PDFs), and ffprobe (videos)
— no LLM, runs in milliseconds. Also opportunistically parses
dimension hints from the filename and compares them to the actual
file, returning a match/mismatch verdict.
Output is a JSON-serializable dict; format_for_llm_prompt() renders it
as a tight Markdown block that downstream prompts can prepend. Module
never raises — inspection errors land in `errors` so partial reports
still surface.
Standalone for this commit. Wiring into the upload flow and UI lands
in subsequent commits on this branch.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
