Implement duplicate suppression and noise-budget engine

[mdheller]

Goal

Implement event coalescing and noise budgeting so repeated low-level records do not become operator-facing garbage.

Scope

• Define event fingerprint algorithm.
• Add duplicate suppression window.
• Add per-daemon/component noise budget fields.
• Track raw-to-canonical event reduction ratio.
• Preserve representative evidence samples.
• Escalate only when repeated events change risk class, not because repetition is noisy.

Acceptance criteria

• Repeated identical denials collapse into one canonical telemetry.coalesced event.
• Coalesced events preserve count, first_seen, last_seen, and sample evidence references.
• Severity is not inflated by duplication alone.
• DeliveryExcellence can consume signal-quality metrics.