fix(avatar): data-color severity optional to acknowledge custom-color escape hatch

Audit caught 4 'missing data-color' violations on the Avatar Provider —
the demo includes consumers passing non-canonical CSS color strings
(`#7c3aed`, `oklch(70% 0.15 220)`, `rgb(245 158 11)`) which the wrapper
correctly routes through `data-color-custom=""` + an inline
`--avatar-color-custom` CSS variable instead of the enum attr.

The morfo enum can't represent arbitrary CSS color strings, so the
`data-color` attr is legitimately absent in those cases. The contract
should reflect that: severity becomes `optional`. Symmetric with the
`Avatar.Badge` part which already declared this attr as optional.

Behaviour unchanged. Only the morfo's severity flag changes.

After this fix `morfo:check`: 6 issues / 3 components → 2 issues / 2
components.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/uix/morfo/components/avatar.ts

@@ -25,6 +25,17 @@ export const avatarMorfo = {
 					value: v.propRef('variant')
 				},
 				{
+					// Optional severity acknowledges the documented escape
+					// hatch: the wrapper accepts any CSS color string
+					// (hex, oklch, rgb, etc.) and routes non-canonical
+					// values through `data-color-custom` + a
+					// `--avatar-color-custom` inline CSS variable instead.
+					// When the consumer passes a canonical role
+					// (`primary`, `affirm`, etc.) the enum value lands
+					// here; when they pass a custom color, this attr is
+					// absent by design (the recipe knows to fall through
+					// to the custom path). Symmetric with `Avatar.Badge`,
+					// which already declared this attr as optional.
 					attr: 'data-color',
 					values: [
 						'primary',
@@ -36,7 +47,8 @@ export const avatarMorfo = {
 						'threat',
 						'loss'
 					],
-					value: v.propRef('color')
+					value: v.propRef('color'),
+					severity: 'optional'
 				},
 				{
 					attr: 'data-radius',