fix(month-grid, year-grid): cell label fallback now renders

The eidos Cell wrapper previously delegated a children snippet that called
`bodyContent?.(snippetProps)`. When the consumer wrote `<Cell {year} />`
without a children snippet, the snippet still resolved to nothing, which
made the soma cell's `{:else} {label}` fallback never fire — cells came
out empty in the DOM.

Move the fallback into the eidos cell's own children snippet:
`{#if bodyContent}{@render bodyContent(...)}{:else}{label}{/if}`.

Verified in browser: MonthGrid renders Jan..Dec with the placeholder
year, YearGrid renders the decade page correctly with data-current on
today's year. svelte-check still 0 errors / 0 warnings / 4572 files.

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

src/uix/eidos/components/month-grid/month-grid-cell.svelte

@@ -7,6 +7,10 @@
 
 <MonthGrid.Cell {...rest}>
 	{#snippet children(snippetProps: MonthGridCellSnippetProps)}
-		{@render bodyContent?.(snippetProps)}
+		{#if bodyContent}
+			{@render bodyContent(snippetProps)}
+		{:else}
+			{snippetProps.label}
+		{/if}
 	{/snippet}
 </MonthGrid.Cell>

src/uix/eidos/components/year-grid/year-grid-cell.svelte

@@ -7,6 +7,10 @@
 
 <YearGrid.Cell {...rest}>
 	{#snippet children(snippetProps: YearGridCellSnippetProps)}
-		{@render bodyContent?.(snippetProps)}
+		{#if bodyContent}
+			{@render bodyContent(snippetProps)}
+		{:else}
+			{snippetProps.label}
+		{/if}
 	{/snippet}
 </YearGrid.Cell>