Harden PAQXOS frame validation

[Ashbrunaugh]

Summary:

• validate PAQXOS frames against manifest-declared detector identifiers
• reject duplicate, mismatched, or ambiguous detector sets with explicit reasons
• preserve missing Copt, reference variation, reverse order, and time gaps as QC flags
• document the generic ingestion contract

Verification:

• source suite: 33 passed
• installed-wheel suite: 33 passed
• manuscript corpus: 126 exports, zero accepted-array differences
• independent Claude Code audit: no Critical or High findings; all three Medium findings addressed and closure-reviewed

Release boundary:

• v0.1.0 tag is unchanged