Control Plane Timeline: Switch to descending date and fallback to mentioned_at for non events

[wsimmonds]

Addresses #55

Introduce effective_date
Instead of using just occurred_start for display/ordering I've introduced an effective_date property to object in the withDates array: This will be occurred_start if present but otherwise will fallback to mentioned_at (or null if not set).

Sort order
It now sorts by effective_date in descending order, which seems to be consistent with the query on the api:

hindsight/hindsight-api/hindsight_api/engine/memory_engine.py

Lines 2082 to 2091 in 6d820ef

	units = await conn.fetch(
	f"""
	SELECT id, text, event_date, context, fact_type, mentioned_at, occurred_start, occurred_end, chunk_id
	FROM memory_units
	{where_clause}
	ORDER BY mentioned_at DESC NULLS LAST, created_at DESC
	LIMIT {limit_param} OFFSET {offset_param}
	""",
	*query_params,
	)

Testing
I've tested this manually with a memory bank of mine, verifying that opinions which previously were hidden now show and are ordered correctly.

[nicoloboschi]

I think it would be better to a UI control (a switch) that let the user see mentioned vs occurred

I think using a effective date might be confusing