M9 section S1, commit 3 — two more shared-toolkit pieces:
- common.iso(dt): the "x.isoformat() if x else None" idiom (repeated 20+ times
across every serializer) as one helper. Adopted in Note.serialize() and the
revision serializer; other serializers adopt it in their sections.
- colors.py: NOTE_COLORS (canonical, on the model) + a single normalize_color().
notes.py now imports the palette + normalizer from here and drops its local
copy. labels.py's identical LABEL_COLORS/_normalize_label_color fold into this
in the Organize section (S3); sync in S4.
normalize_color and NOTE_COLORS remain importable from thoughtsync.notes (used by
tests + sync), so nothing downstream breaks. common has no in-app imports, so the
model→common→colors chain has no cycle. Behavior-preserving.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FRgehjoz7Yv8LkUfADxACm
