feat(ai): AI Workspace per job application — modules + append-only history

Phase 5 backend. A unified AI Workspace for each application, orchestrating the
five suggestion modules through the existing ISummarizerService provider
abstraction and storing every generation as append-only history (AiInteraction)
so outputs can be reused, compared, and deleted — distinct from the existing
AiWorkspaceNote cache (one row, overwritten).

Modules (all suggestion-only, "never invent facts" guardrail, never mutate the
profile/variant/application): job-analysis, career-match, cover-letter (6 modes),
interview, application-review. Each builds a prompt from the job + master profile
text and returns markdown.

- Models/AiInteraction.cs + migration AddAiInteractions (verified on container)
- Services/AiWorkspaceService.cs (prompts, history, delete)
- Controllers/AiWorkspaceController.cs (/api/jobapplications/{id}/ai:
  generate, history, delete, modules+provider)
- 7 tests (store, history filter/order, delete, mode normalization, unknown
  module, empty output, tenant scoping); 306 backend green

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

JobTrackerApi/Migrations/JobTrackerContextModelSnapshot.cs

@@ -17,6 +17,50 @@ namespace JobTrackerApi.Migrations
 #pragma warning disable 612, 618
             modelBuilder.HasAnnotation("ProductVersion", "9.0.14");
 
+            modelBuilder.Entity("JobTrackerApi.Models.AiInteraction", b =>
+                {
+                    b.Property<int>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("INTEGER");
+
+                    b.Property<DateTimeOffset>("CreatedAtUtc")
+                        .HasColumnType("TEXT");
+
+                    b.Property<int>("JobApplicationId")
+                        .HasColumnType("INTEGER");
+
+                    b.Property<string>("Mode")
+                        .HasColumnType("TEXT");
+
+                    b.Property<string>("Module")
+                        .IsRequired()
+                        .HasColumnType("TEXT");
+
+                    b.Property<string>("OwnerUserId")
+                        .IsRequired()
+                        .HasColumnType("TEXT");
+
+                    b.Property<string>("Provider")
+                        .IsRequired()
+                        .HasColumnType("TEXT");
+
+                    b.Property<string>("ResultJson")
+                        .IsRequired()
+                        .HasColumnType("TEXT");
+
+                    b.Property<string>("Title")
+                        .IsRequired()
+                        .HasColumnType("TEXT");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("JobApplicationId");
+
+                    b.HasIndex("OwnerUserId", "JobApplicationId", "Module", "CreatedAtUtc");
+
+                    b.ToTable("AiInteractions");
+                });
+
             modelBuilder.Entity("JobTrackerApi.Models.AiWorkspaceNote", b =>
                 {
                     b.Property<int>("Id")
@@ -1766,6 +1810,17 @@ namespace JobTrackerApi.Migrations
                     b.ToTable("AspNetUserTokens", (string)null);
                 });
 
+            modelBuilder.Entity("JobTrackerApi.Models.AiInteraction", b =>
+                {
+                    b.HasOne("JobTrackerApi.Models.JobApplication", "JobApplication")
+                        .WithMany()
+                        .HasForeignKey("JobApplicationId")
+                        .OnDelete(DeleteBehavior.Cascade)
+                        .IsRequired();
+
+                    b.Navigation("JobApplication");
+                });
+
             modelBuilder.Entity("JobTrackerApi.Models.AiWorkspaceNote", b =>
                 {
                     b.HasOne("JobTrackerApi.Models.JobApplication", "JobApplication")