fix(read): detect binary files and prevent empty output on filter failure

- Detect binary files (null bytes in first 8KB) before filtering
- Show clear message: [binary file] path (size) instead of empty output
- Fallback to raw content if filter produces empty output on non-empty file
- Prevents LLM from concluding a 70MB file is "empty" (was #822)

Fixes #822

Signed-off-by: Patrick szymkowiak <patrick.szymkowiak@innovtech.eu>