Add legal indicators whitelist to gibberish detection

[VaaishnaviS]

Fixes #4676

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I have implemented a whitelist-based "Safe Gate" for gibberish detection.

The Problem: The normalize() function was stripping non-alphanumeric characters like ©, (c), and @. This caused the Markov chain model to see only fragments of legal strings, leading to high "gibberish" scores.

The Fix: Added a COPYRIGHT_INDICATORS list that is checked before normalization occurs. If a match is found, the string is immediately flagged as "not gibberish," bypassing the math model entirely. This is more robust and faster for legal text.

Signed-off-by: VaaishnaviS [email protected]