fix(memory): add exact-duplicate dedup to SemanticStore.store()

[kagura-agent]

Problem

Closes #125.

extractFactsFromSession generates a new crypto.randomUUID() for each fact on every consolidation run. Since findContradictions() explicitly excludes same-object facts (existingObject !== newFact.object), identical-text facts accumulate as separate Qdrant points across sessions.

This leads to the system prompt's Known Facts section containing multiple copies of the same fact (e.g. four copies of "No let's not worry about being a repeat contributor...").

Fix

Add findExactDuplicate() to SemanticStore that scrolls Qdrant for an existing valid fact with the same subject + object (both keyword-indexed). When a duplicate exists, store() merges source_episode_ids into the existing fact via updatePayload() and returns early — skipping the upsert of a new point.

Changes

• src/memory/semantic.ts: Add object keyword payload index, add findExactDuplicate() method, add dedup check in store() between contradiction resolution and upsert
• src/memory/__tests__/semantic.test.ts: Add tests for dedup-and-merge path and different-object-creates-new-point path; update existing store test to mock the scroll endpoint

Testing

bun test src/memory/__tests__/semantic.test.ts
# 7 pass, 0 fail

Full suite: 2368 pass, 7 fail (pre-existing, same on main).

[kagura-agent]

Closing — based on maintainer merge patterns, external PRs aren't being merged here. The fix is available in the branch if useful. Thanks!