Persistence Query — multi-tag filter (intersect / union)

[pathosDev]

`PersistenceQuery.eventsByTag` (#36) returns events with a single tag. Real workloads often want to combine tags: "all events tagged `type:Order` AND `tenant:t1`" or "tagged either `tenant:t1` OR `tenant:t2`".

Today users have to:

• Query each tag separately and merge in app code.
• Or (worse) emit pre-combined synthetic tags at write time.

API sketch:

```ts
query.eventsByTag({ all: ['type:Order', 'tenant:t1'] }) // intersect
query.eventsByTag({ any: ['tenant:t1', 'tenant:t2'] }) // union
query.eventsByTag({ all: ['type:Order'], not: ['archived'] }) // exclusion
```

Scope:

• Implementations:
  • InMemoryQuery: trivial — filter the event stream in memory.
  • SqliteQuery (using SQLite tags join table for indexed tag queries #43's tags side-table): JOIN on multiple tag rows with HAVING COUNT.
  • CassandraQuery (after Cassandra events_by_tag side-table for indexed tag queries #44 lands): partial intersect via `IN` + app-side filter.

Out of scope:

• Time-range filters combined with tags — separate sub-issue if needed.

Estimate: 1-2 days.