fix(aep): Date.now() timestamps + addAction capability_decision sync

[HainingYin]

Summary

• bug(@wasmagent/aep): emit() defaults to performance.now() instead of Date.now() causing created_at_ms ≈ 19ms #14 fix: Replace performance.now() with Date.now() in emit(), build(), and addAction(). performance.now() returns ms-since-process-start (~730), not Unix epoch — downstream tools showed 1970-01-01 for all records.
• dx(@wasmagent/aep): addAction() with capability_decision should automatically register to capability_decisions[] — split API causes silent empty manifest #15 fix: addAction() with capability_decision now auto-registers to record-level capability_decisions[] (deduped by capability+subject+resource). Previously the split API caused toEvents() to produce zero policy_decision events.

Test plan

• Existing AEP emitter tests pass
• emit() without explicit timestamp produces created_at_ms in reasonable epoch range (e.g. >1700000000000)
• addAction({ capability_decision: {...} }) populates capability_decisions[] without separate addCapabilityDecision() call
• Duplicate capability decisions (same capability+subject+resource) are not double-registered

Fixes #14, #15

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