Add recipient preference filtering for access notifications

[felixbeer]

Problem

Access notification preview exists, but recipient preference filtering (opt-in/opt-out/context) is missing.

Scope

• Add recipient preference filtering hooks/strategies.
• Support opt-in/opt-out and context-aware filtering.
• Keep existing recipient preview, but ensure it reflects filtered recipients accurately.

Out of scope

• Rebuilding the existing preview UI from scratch.

Acceptance criteria

• Notification action can apply preference filters without custom action rewrites.
• Preview output matches final filtered recipient set.