Implements two new temporal query methods on MnemosyneArchive:
- by_date_range(start, end): returns entries whose created_at falls within
an ISO datetime range (inclusive, timezone-naive inputs treated as UTC)
- temporal_neighbors(entry_id, window_days=7): returns entries created
within N days of a given anchor entry, excluding the anchor itself
Both methods return results sorted by created_at ascending and handle
edge cases: empty archive, single entry, timezone-naive dates, boundary
dates, and missing entry IDs (temporal_neighbors raises KeyError).
Adds CLI subcommands:
- mnemosyne timeline <start> <end>
- mnemosyne neighbors <entry_id> [--days N]
Tests cover: empty results, boundary inclusivity, timezone handling,
window sizing, sort order, and error cases.
Fixes#1244
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
