Add date/time filtering to mempalace_search

[nautis]

Problem

Semantic search is poor at temporal queries. Searching for "what did we discuss today" or "April 9 2026" returns low similarity scores (0.35 best) even when matching drawers exist. This is a fundamental limitation of embedding-based search — dates aren't semantically meaningful.

Proposal

Add optional time-based filters to mempalace_search and the mempalace search CLI:

mempalace search "auth decisions" --after 2026-04-01
mempalace search "auth decisions" --last 7d
mempalace search "auth decisions" --between 2026-03-01 2026-04-01

MCP tool equivalent:

{
  "query": "auth decisions",
  "after": "2026-04-01",
  "before": "2026-04-10"
}

ChromaDB supports metadata filtering via where clauses. If drawers already store a timestamp in metadata, this is a straightforward addition. If not, adding created_at to drawer metadata at ingest time would enable it.

Why this matters

"What did we discuss this week?" and "what changed since last sprint?" are among the most common memory queries. Right now they effectively don't work.

[web3guru888]

+1. This is one of the biggest gaps for any integration doing temporal reasoning.

Our specific pain point:

We run multi-day discovery cycles across 5 domains. A common query pattern is "what did we discover in astrophysics this cycle?" — meaning the last 3-7 days. Today, we have to:

1. search_memories("astrophysics discoveries", wing="astrophysics") — returns results from all time
2. Client-side, fetch each result's metadata to check dates
3. Filter manually

This turns a single query into N+1 round-trips. With --after support, it's one call.

Proposed API shape looks right, one addition:

The --last 7d relative syntax is essential — most temporal queries are relative ("this week", "this sprint"), not absolute dates. I'd also suggest supporting --last 1h for the "what just got mined" use case, which is common right after running mempalace mine on a new codebase.

Implementation note:

This depends on created_at being stored in ChromaDB metadata at ingest time (see #465). If it's already there, the ChromaDB where clause is straightforward:

where={"created_at": {"$gte": after_timestamp}}

If created_at isn't in metadata yet, both this issue and #465 need the same prerequisite: adding the timestamp to the metadata dict in add_drawer. Worth solving both together.

[mvalentsev]

Opened #2000 with a since/before window for search (MCP tool + CLI).