feat(mui): fixed-width DataTable columns + restore Projects next-number hint

DataTable: optional per-column width; when any column sets one, the table uses table-layout:fixed with a colgroup so columns keep a stable size instead of reflowing as rows are filtered (overflow clipped with ellipsis). Tables without widths keep auto layout. Projects: assign column widths; restore the original '(přiděleno automaticky)' suffix on the next-number hint.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/admin/pages/Projects.tsx

@@ -245,6 +245,7 @@ export default function Projects() {
     {
       key: "project_number",
       header: "Číslo",
+      width: "12%",
       sortKey: "project_number",
       mono: true,
       render: (p) => p.project_number,
@@ -252,6 +253,7 @@ export default function Projects() {
     {
       key: "name",
       header: "Název",
+      width: "16%",
       sortKey: "name",
       bold: true,
       render: (p) => p.name || "—",
@@ -259,16 +261,19 @@ export default function Projects() {
     {
       key: "customer",
       header: "Zákazník",
+      width: "13%",
       render: (p) => p.customer_name || "—",
     },
     {
       key: "responsible",
       header: "Zodpovědná osoba",
+      width: "14%",
       render: (p) => p.responsible_user_name || "—",
     },
     {
       key: "status",
       header: "Stav",
+      width: "10%",
       sortKey: "status",
       render: (p) => (
         <StatusChip
@@ -280,6 +285,7 @@ export default function Projects() {
     {
       key: "order",
       header: "Objednávka",
+      width: "12%",
       render: (p) =>
         p.order_id ? (
           <Box
@@ -300,18 +306,21 @@ export default function Projects() {
     {
       key: "start_date",
       header: "Začátek",
+      width: "8%",
       mono: true,
       render: (p) => formatDate(p.start_date),
     },
     {
       key: "end_date",
       header: "Konec",
+      width: "8%",
       mono: true,
       render: (p) => formatDate(p.end_date),
     },
     {
       key: "actions",
       header: "Akce",
+      width: "7%",
       align: "right",
       render: (p) => (
         <Box sx={{ display: "flex", gap: 0.5, justifyContent: "flex-end" }}>
@@ -443,7 +452,7 @@ export default function Projects() {
           nextNumberQuery.data?.number ??
           nextNumberQuery.data?.next_number ??
           "…"
-        }`}
+        } (přiděleno automaticky)`}
         submitText="Vytvořit"
         loading={creating}
       >