Implement S03 follow-up draft context loop

.gsd/milestones/M001/slices/S03/tasks/T01-SUMMARY.md

@@ -0,0 +1,28 @@
+---
+title: T01 summary
+status: done
+files:
+  - JobTrackerApi/Controllers/JobApplicationsController.cs
+  - JobTrackerApi.Tests/JobApplicationsFollowUpDraftTests.cs
+verification:
+  - $HOME/.dotnet/dotnet build JobTrackerApi/JobTrackerApi.csproj
+  - docker run --rm -v "$PWD":/src -w /src mcr.microsoft.com/dotnet/sdk:9.0 bash -lc '...dotnet test /tmp/followuptests/FollowUpTests.csproj...'
+---
+
+Strengthened follow-up draft generation so it now consumes imported thread context and saved application package material instead of relying mostly on job summary text.
+
+What changed:
+- `JobTrackerApi/Controllers/JobApplicationsController.cs`
+  - expanded `FollowUpDraftDto` to expose context summary, context signals, thread subject, and last-correspondence metadata for the workspace
+  - added helpers to parse the saved application-answer draft from notes, derive reply-style subjects from the latest thread, and assemble follow-up context signals from recruiter/package/thread state
+  - enriched `GetFollowUpDraft(...)` so the AI prompt now includes imported correspondence context, recruiter details, saved tailored CV / cover letter / recruiter message / application-answer material, and thread-stage cues
+  - improved the fallback body so it still reflects saved/thread context when AI output is unavailable
+- `JobTrackerApi.Tests/JobApplicationsFollowUpDraftTests.cs`
+  - added focused backend proof that follow-up draft generation reflects imported thread and saved package state
+
+Verification:
+- Backend host build passed with `$HOME/.dotnet/dotnet build JobTrackerApi/JobTrackerApi.csproj`
+- Focused follow-up draft backend test passed in an isolated Docker harness (`1 passed`)
+
+Important caveat:
+- The broader `JobTrackerApi.Tests` project still has unrelated compile drift, so focused follow-up verification was isolated rather than run through the full test project.