Adds a UtcDateTime TypeDecorator (models.py) that enforces aware-UTC on
write and stamps tzinfo=UTC on read. Replaces 26 DateTime column
declarations. Removes 5 production sites that defensively stripped tzinfo
to match SQLite's lossy round-trip. auth.py now coerces legacy session
cookies upward (stamp UTC on parsed naive marker) instead of stripping
live aware markers downward.
The change is Python-side only: UtcDateTime.impl = DateTime, so DDL and
emitted SQL are unchanged. No Alembic migration needed.
Adds 2 unit tests in test_models.py pinning the decorator's contract
independently of the column declarations.
The three deliberately-naive test_timeago.py fixtures (lines 67, 73, 113)
remain naive on purpose -- they exercise _ensure_utc's normalize-up path
at the public filter boundary, which stays as belt-and-braces defense.
See docs/superpowers/specs/2026-05-16-tz-aware-datetime-design.md.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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