fix: skip audio files from text extraction to prevent binary processing (#7475)

* fix: skip audio files from text extraction early

Audio files should not be processed through extractFileBlocks for text
extraction - they are handled by the dedicated audio transcription
capability (STT).

Previously, audio files were only skipped if they didn't "look like text"
(looksLikeUtf8Text check). This caused issues where some audio binary
data (e.g., long Telegram voice messages) could accidentally pass the
heuristic check and get processed as text content.

This fix:
1. Adds audio to the early skip alongside image/video (more efficient)
2. Removes the redundant secondary check that had the flawed condition

Fixes audio binary being incorrectly processed as text in Telegram and
other platforms.

* Media: skip binary media in file extraction (#7475) (thanks @AlexZhangji)

---------

Co-authored-by: Shakker <shakkerdroid@gmail.com>

CHANGELOG.md

@@ -15,6 +15,7 @@ Docs: https://docs.openclaw.ai
 
 - fix(agents): validate AbortSignal instances before calling AbortSignal.any() (#7277) (thanks @Elarwei001)
 - fix(webchat): respect user scroll position during streaming and refresh (#7226) (thanks @marcomarandiz)
+- Media understanding: skip binary media from file text extraction. (#7475) Thanks @AlexZhangji.
 - Security: guard skill installer downloads with SSRF checks (block private/localhost URLs).
 - Media understanding: apply SSRF guardrails to provider fetches; allow private baseUrl overrides explicitly.
 - Tests: stub SSRF DNS pinning in web auto-reply + Gemini video coverage. (#6619) Thanks @joshp123.