feat(ux): first-time onboarding, empty states, and copy fixes

Implements the six "propose first" items from the product/UX review:

- "/" now redirects to /dashboard instead of the empty /jobs table --
  a new user's first screen is now an overview with orientation, not
  a data table with zero rows and four filter dropdowns.
- Jobs table gets a real first-time empty state (distinct from "no
  results match your filters") pointing at Add Job and the bookmarklet,
  instead of a bare "No jobs found."
- Match Score card and Candidate Fit tab now each get a one-line
  caption explaining what they are and how they differ (deterministic
  keyword coverage vs. AI opinion) -- they previously sat side by side
  with no explanation of why there are two.
- Google sign-in hint now reflects self-serve signup when
  Auth:AllowRegistration is on, instead of always implying you need an
  existing linked account.
- Quick Search button now shows its keyboard shortcut (Ctrl+K / ⌘K)
  inline instead of being undiscoverable.

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

@@ -110,6 +110,19 @@ function parseTags(raw?: string | null): string[] {
 }
 
 
+function EmptyJobsState({ firstTime, onOpenSettings, t }: { firstTime: boolean; onOpenSettings: () => void; t: (key: any) => string }) {
+  if (!firstTime) {
+    return <Typography sx={{ py: 2, textAlign: "center", color: "text.secondary" }}>{t("jobTableNoJobsFound")}</Typography>;
+  }
+  return (
+    <Box sx={{ py: 4, textAlign: "center" }}>
+      <Typography sx={{ fontWeight: 800, mb: 0.5 }}>{t("jobTableEmptyFirstTimeTitle")}</Typography>
+      <Typography sx={{ color: "text.secondary", mb: 1.5, maxWidth: 440, mx: "auto" }}>{t("jobTableEmptyFirstTimeBody")}</Typography>
+      <Button variant="text" onClick={onOpenSettings}>{t("jobTableEmptyFirstTimeBookmarklet")}</Button>
+    </Box>
+  );
+}
+
 function generateOverview(job: JobApplication): string {
   if (job.fullSummary) return job.fullSummary;
   if (job.shortSummary) return job.shortSummary;
@@ -220,6 +233,12 @@ export default function JobTable({ refreshToken, pageSize, onPageSizeChange, col
     return jobs.filter((job) => needsWorkflowWork(job));
   }, [jobs, readinessFilter]);
 
+  // Distinguishes "you have zero jobs, period" from "no results match your filters" so the
+  // empty state can actually help a first-time user instead of just saying "nothing here".
+  const noFiltersActive = !debouncedSearch.trim() && statusFilter === "All" && companyFilterId === "All"
+    && !debouncedLocation.trim() && !needsFollowUpOnly && readinessFilter === "all";
+  const isFirstTimeEmpty = mode === "jobs" && total === 0 && noFiltersActive;
+
   const selectedIdSet = useMemo(() => new Set(selectedIds), [selectedIds]);
 
   const selectedAllOnPage = filteredJobs.length > 0 && filteredJobs.every((job) => selectedIdSet.has(job.id));
@@ -629,7 +648,9 @@ export default function JobTable({ refreshToken, pageSize, onPageSizeChange, col
                 </Paper>
               );
             })}
-            {filteredJobs.length === 0 && !jobsResource.loading && !jobsResource.error ? <Typography sx={{ py: 2, textAlign: "center" }}>{t("jobTableNoJobsFound")}</Typography> : null}
+            {filteredJobs.length === 0 && !jobsResource.loading && !jobsResource.error ? (
+              <EmptyJobsState firstTime={isFirstTimeEmpty} onOpenSettings={() => navigate("/settings")} t={t} />
+            ) : null}
           </Stack>
         ) : (
           <Box sx={{ overflowX: "auto" }}>
@@ -721,7 +742,9 @@ export default function JobTable({ refreshToken, pageSize, onPageSizeChange, col
                     </React.Fragment>
                   );
                 })}
-                {filteredJobs.length === 0 && !jobsResource.loading && !jobsResource.error ? <TableRow><TableCell colSpan={visibleDesktopColumns}><Typography sx={{ py: 2, textAlign: "center" }}>{t("jobTableNoJobsFound")}</Typography></TableCell></TableRow> : null}
+                {filteredJobs.length === 0 && !jobsResource.loading && !jobsResource.error ? (
+                  <TableRow><TableCell colSpan={visibleDesktopColumns}><EmptyJobsState firstTime={isFirstTimeEmpty} onOpenSettings={() => navigate("/settings")} t={t} /></TableCell></TableRow>
+                ) : null}
               </TableBody>
             </Table>
           </Box>