feat(workspace): Application Workspace foundation (Phase 5 milestone 1)

Every JobApplication gets a dedicated workspace at /applications/{id} — a
surface, not a new data store. It owns no data and duplicates none: CV comes
from the Phase 4 CvVariant lens, analysis/match/interview from the existing
AiWorkspacePanel, documents from Attachments, communication from
Correspondence, activity from JobEvent, stage semantics from JobPipeline. No
career data is copied and nothing here writes.

- GET /api/jobapplications/{id}/workspace: one aggregate read (role, company,
  stage, dates, attached CV variant, cover letter, documents, AI history,
  recent activity) replacing the page fanning out across endpoints
- Next recommended action: ordered rules answering "what do I do next?", the
  core product principle for this phase
- ApplicationWorkspacePage: left nav + linkable ?section=, reusing the existing
  component for each domain; later-milestone sections say so rather than faking
- Entry point from the job dialog via an optional onOpenWorkspace callback —
  the dialog must not depend on router context (it is mounted without a
  <Router> in several suites), so the caller owns navigation
- 8 backend tests (aggregate, CV variant surfacing, counts, activity ordering,
  next-step rules, tenant scoping)

Local: 314 backend, 88/88 frontend (31 suites), tsc clean, production build ok.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

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

@@ -50,6 +50,9 @@ interface Props {
   onClose: () => void;
   initialTab?: number;
   initialFollowUpMode?: string;
+  // Supplied by callers that live inside the router. Optional on purpose: the dialog must not depend
+  // on router context, so it stays renderable standalone (and in tests) without a <Router>.
+  onOpenWorkspace?: (jobId: number) => void;
 }
 
 function statusChipColor(status: string): "default" | "primary" | "warning" | "error" | "success" {
@@ -128,7 +131,7 @@ function serializeTailoredDraft(draft: TailoredCvDraft) {
   });
 }
 
-export default function JobDetailsDialog({ open, jobId, onClose, initialTab = 0, initialFollowUpMode }: Props) {
+export default function JobDetailsDialog({ open, jobId, onClose, initialTab = 0, initialFollowUpMode, onOpenWorkspace }: Props) {
   const { toast } = useToast();
   const { t } = useI18n();
   const { confirmAction } = useDialogActions();
@@ -680,6 +683,12 @@ export default function JobDetailsDialog({ open, jobId, onClose, initialTab = 0,
           }}
         >
           <Typography variant="body2" sx={{ color: "text.secondary" }}>{summaryFirstText}</Typography>
+          {/* Phase 5: the full-page Application Workspace. The dialog stays as the quick view. */}
+          {jobId && onOpenWorkspace ? (
+            <Button size="small" variant="outlined" sx={{ mt: 1.5 }} onClick={() => onOpenWorkspace(jobId)}>
+              Open application workspace
+            </Button>
+          ) : null}
         </Box>
         <Tabs
           value={tab}