fix(memory-graph): stop painting expired memories as expiring

[abhay-codes07]

Problem

getMemoryBorderColor decides the expiring border from the time left until forgetAfter:

if (mem.forgetAfter) {
  const msLeft = new Date(mem.forgetAfter).getTime() - Date.now()
  if (msLeft < SEVEN_DAYS_MS) return colors.memBorderExpiring
}

msLeft < SEVEN_DAYS_MS is meant to catch "expires within the next week", but it is also true for every forgetAfter in the past, where msLeft is negative. So a memory whose forget time has already elapsed, but which the server has not yet swept to isForgotten, keeps the expiring border forever. It reads as "about to expire" indefinitely instead of as a normal or already-expired node, and the closer to the past it gets the more wrong the signal is.

Fix

Require that there is actually time left before marking a memory expiring:

if (msLeft > 0 && msLeft < SEVEN_DAYS_MS) return colors.memBorderExpiring

Elapsed memories fall through to the existing recency / default branch, which matches how an unremarkable node is drawn. The isForgotten early return above is unchanged, so anything already marked forgotten still gets the forgotten color first.

Test

Added a case to graph-data-utils.test.ts for a memory with a forgetAfter a minute in the past and an old createdAt: it now resolves to memStrokeDefault rather than memBorderExpiring. Full package suite passes and tsc --noEmit is clean.

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