fix(redaction): fully redact whitespace-separated auth credentials

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Motivation

• A recent change to redact_text stopped assignment redaction at the first whitespace, which left credential tokens in values like Authorization: Basic <credential> unredacted and leaked into report evidence.

Description

• Adjusted the unquoted assignment regex in redact_text to allow an optional second whitespace-delimited token so two-part auth schemes (e.g., Basic <credential>) are fully consumed and redacted.
• Kept existing provider-specific redaction intact (e.g., Bearer and known token shapes) and preserved surrounding context behavior (so unrelated trailing text like paths remain visible).
• Added a focused regression test redacts_basic_auth_values_after_sensitive_keys to ensure Authorization: Basic ... values are fully redacted.

Testing

• Ran the unit tests for the core crate focusing on redaction with cargo test -p nightward-core redacts_, and the redaction-related tests passed (6 passed; 0 failed).
• The new regression test redacts_basic_auth_values_after_sensitive_keys was executed as part of that run and passed.

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Codex Task