The server's palette is checked against the shared fixture's hues

The web already checked its tint keys against grammar.json; the server's
NOTE_COLORS, which normalize_color accepts, had no such guard. It is now the
fixture's hues plus "default". The core has no palette to check: it stores
whatever the UI (which only offers palette keys) or the server sends.

DRY pass #2, batch 3 (#5372).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_grammar_fixture.py

@@ -12,6 +12,7 @@ from pathlib import Path
 
 import pytest
 
+from inkwell.colors import NOTE_COLORS
 from inkwell.notes.checklist import parse_items, render_item
 from inkwell.notes.helpers import derive_display_title
 from inkwell.notes.recurrence import REMINDER_RECURRENCES
@@ -52,3 +53,9 @@ def test_display_titles(case):
 
 def test_recurrences():
     assert REMINDER_RECURRENCES == set(FIXTURE["recurrences"])
+
+
+def test_palette_keys():
+    """The palette the server accepts is the fixture's hues plus `default`, the key
+    unrecognised input lands on. The web checks the same hues (DERIVED_TINT_KEYS)."""
+    assert NOTE_COLORS == {"default", *FIXTURE["tint"]["keys"]}