fix(events): search permitted knowledge sources

[dajiaohuang]

Follow-up to #13

The D&D integration showed that actor-visible history also includes events referenced by the actor's current knowledge heads, even when the event has no explicit participant row. The first actor-event search covered participant events only.

This follow-up:

• optionally includes source events from current actor-knowledge heads
• requires callers to provide the permitted disclosure scopes
• preserves branch-head filtering
• keeps participant-only behavior as the default
• verifies that owner knowledge is included only when requested and excluded for a DM-only scope filter

Verification

• uv run pytest — 325 passed, 14 skipped
• uv run ruff check .
• git diff --check

Completes #13.