style(ui): float remaining table/card containers to design system

Repo-wide sweep for the same flat 1px-border "fake card" pattern
already fixed in Dashboard/Kanban/JobDetailsDialog/auth pages this
session -- AddJobModal, Attachments, CompaniesTable, Correspondence,
EditJobDialog, and the admin audit/system/users pages all had a table
container or content box using border+divider instead of the
floating-shadow treatment used everywhere else now.

Left AppShell.tsx/App.tsx alone -- their border:1px+divider instances
are icon-button and badge outlines, not card containers; that's a
different, correct use of the pattern.

job-tracker-ui/src/components/CompaniesTable.tsx

@@ -157,7 +157,7 @@ export default function CompaniesTable() {
             ) : null}
           </Stack>
         ) : (
-          <TableContainer sx={{ borderRadius: 3, border: "1px solid", borderColor: "divider" }}>
+          <TableContainer sx={{ borderRadius: 3, border: "none", boxShadow: "0px 1px 2px 0px rgba(15,23,42,0.04), 0px 8px 24px -12px rgba(15,23,42,0.12)" }}>
             <Table>
               <TableHead>
                 <TableRow>