feat(workspace): unified application checklist (Phase 5 milestone 2)

Evolve the existing readiness workflow into one persisted, user-controlled
checklist rather than adding a second tracker.

ApplicationChecklistItem records only completion state and user intent. Each
default system item carries a stable SystemKey and an AutoSignal — the same
signal /readiness already computed — and re-syncs on every read: a satisfied
signal auto-completes the item, a reverted signal reopens it, and a manual tick
always wins. Users can add, reorder, dismiss and delete.

Readiness is refactored into a projection of the checklist (score = completion
percentage, completed/missing = live items by status). Its DTO shape and the
workflowSignal/reminders health view are unchanged, so no API contract breaks.

The workspace's next recommended action now comes from the first pending
checklist item in category priority order (preparation, submission, follow-up,
interview, custom), replacing the parallel ruleset — so the overview can never
recommend something already ticked off, and a user's own task can be next.

The table follows the established MariaDB-safe path: the scaffolded migration is
a no-op and the idempotent reconciler owns the DDL for both providers. Verified
on MariaDB 11 — auto_increment PK, varchar/datetime(6)/tinyint(1) columns, both
indexes inside the key limit, cascade delete, unique system key per application,
and NULL system keys not colliding for custom items.

329 backend tests, 94 frontend tests, type check, production build and both
Docker builds pass locally.

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

job-tracker-ui/src/views/ApplicationWorkspacePage.tsx

@@ -12,11 +12,13 @@ import DescriptionOutlinedIcon from "@mui/icons-material/DescriptionOutlined";
 import MailOutlineIcon from "@mui/icons-material/MailOutline";
 import FolderOutlinedIcon from "@mui/icons-material/FolderOutlined";
 import AutoFixHighIcon from "@mui/icons-material/AutoFixHigh";
+import ChecklistIcon from "@mui/icons-material/Checklist";
 
 import { getApiErrorMessage } from "../api";
 import Attachments from "../components/Attachments";
 import Correspondence from "../components/Correspondence";
 import AiWorkspacePanel from "../components/AiWorkspacePanel";
+import ApplicationChecklist from "../components/ApplicationChecklist";
 import {
   WORKSPACE_SECTIONS, WorkspaceOverview, WorkspaceSectionKey, applicationWorkspaceApi,
 } from "../applicationWorkspace";
@@ -101,7 +103,10 @@ export default function ApplicationWorkspacePage() {
         {section === "communication" && jobId > 0 && (
           <Paper sx={{ p: 2, borderRadius: 3 }}><Correspondence jobId={jobId} job={null as any} /></Paper>
         )}
-        {["checklist", "cv", "cover-letter", "portfolio", "timeline", "notes"].includes(section) && (
+        {section === "checklist" && jobId > 0 && (
+          <ApplicationChecklist jobId={jobId} onChanged={load} />
+        )}
+        {["cv", "cover-letter", "portfolio", "timeline", "notes"].includes(section) && (
           <ComingInMilestone section={section} />
         )}
       </Box>
@@ -146,6 +151,7 @@ function OverviewSection({ overview, onGo, onReload }: {
     { icon: <MailOutlineIcon fontSize="small" />, label: "Cover letter", value: overview.hasCoverLetter ? "Ready" : "Not written", ok: overview.hasCoverLetter, go: "cover-letter" as const },
     { icon: <FolderOutlinedIcon fontSize="small" />, label: "Documents", value: overview.documentCount ? `${overview.documentCount} attached` : "None", ok: overview.documentCount > 0, go: "documents" as const },
     { icon: <AutoFixHighIcon fontSize="small" />, label: "AI suggestions", value: overview.aiInteractionCount ? `${overview.aiInteractionCount} saved` : "None yet", ok: overview.aiInteractionCount > 0, go: "analysis" as const },
+    { icon: <ChecklistIcon fontSize="small" />, label: "Checklist", value: overview.checklistProgress ? `${overview.checklistProgress.completed}/${overview.checklistProgress.total} done` : "—", ok: (overview.checklistProgress?.percent ?? 0) === 100, go: "checklist" as const },
   ] : [], [overview]);
 
   if (!overview) {
@@ -170,7 +176,7 @@ function OverviewSection({ overview, onGo, onReload }: {
         </Alert>
       )}
 
-      <Box sx={{ display: "grid", gridTemplateColumns: { xs: "1fr 1fr", md: "repeat(4, 1fr)" }, gap: 1.5 }}>
+      <Box sx={{ display: "grid", gridTemplateColumns: { xs: "1fr 1fr", md: "repeat(5, 1fr)" }, gap: 1.5 }}>
         {stats.map((s) => (
           <Paper key={s.label} variant="outlined" role="button" tabIndex={0}
             onClick={() => onGo(s.go)}