feat: Phase 0 foundation — Job entity, expanded pipeline, AI service lockdown, DateApplied history

Unblocks the documented core workflow and closes the AI-service exposure,
without changing existing behaviour.

Job/JobApplication split (additive; see ADR-002):
- New Job entity (the opportunity) with owner-scoped query filter; nullable
  JobApplication.JobId FK. Nothing reads Job yet.
- Migration AddJobEntityAndProspectStages, hand-edited to drop reconciler-owned
  tables the scaffolder re-emitted; verified against the real dev DB.

Pipeline: 10 internal stages across three concerns kept separate —
PipelineStage (workflow) / PipelineGroup (UI: NotApplied/Active/Closed) /
PipelineCategory (analytics). Adds Saved/Interested/Preparing/Withdrawn;
keeps Waiting and Ghosted. Kanban shows 3 grouped columns; cards keep a stage
chip and full transitions; drag applies only safe transitions (never infers
Ghosted/Withdrawn).

DateApplied nullable + SavedAt. Cleared when leaving Applied so analytics stay
accurate; the discarded date is preserved as an AppliedDateCleared JobEvent.

AI service lockdown: no host port; private ai_internal network (backend is the
only other member); X-Ai-Service-Token required on all non-/health endpoints;
AI_SERVICE_TOKEN mandatory via compose. Verified backend-only against the live
stack.

Also carries two pre-existing working-tree files (views/ProfilePage.tsx,
views/CareerWorkspacePage.tsx) so the tree is clean for the branch integration.

Tests: +40 backend (247 total), +5 sidecar (16), +15 frontend.

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

JobTrackerApi/Services/FollowUpReminderHostedService.cs

@@ -92,7 +92,9 @@ public sealed class FollowUpReminderHostedService : BackgroundService
             var followMode = SuggestFollowUpMode(job.Status);
             var detailsUrl = $"{baseUrl}/jobs?open={job.Id}&tab=4&followMode={Uri.EscapeDataString(followMode)}";
             var companyName = job.Company?.Name ?? "Unknown company";
-            var appliedOn = job.DateApplied.ToString("MMMM d, yyyy");
+            // RulesEngine never raises a follow-up for a job with no DateApplied, so this should
+            // always have a value; the fallback just keeps the email readable rather than throwing.
+            var appliedOn = job.DateApplied?.ToString("MMMM d, yyyy") ?? "an unrecorded date";
             var subject = $"Follow up reminder: {job.JobTitle} at {companyName}";
             var body = string.Join("\n\n", new[]
             {