feat: complete release readiness work

- consolidate API ownership and remove dead vendor code

- add Stripe billing, learning paths, and public CV hardening

- add migration, recovery, security, audit, and browser gates

JobTrackerApi/Models/AiWorkspaceNote.cs

@@ -0,0 +1,19 @@
+namespace JobTrackerApi.Models;
+
+// Generic persistence for per-job AI workspace outputs whose shape is irregular/nested enough
+// that per-field columns (as used by InterviewPrepNote) would be unreasonable -- candidate fit
+// and focus plan each make several AI calls and return DTOs with 6-13 fields including nested
+// objects. One row per (owner, job, note type); ResultJson is the serialized DTO. See
+// career-workspace-implementation-roadmap.md Phase F5 -- "persist interview prep / fit outputs".
+public sealed class AiWorkspaceNote
+{
+    public int Id { get; set; }
+    public string OwnerUserId { get; set; } = string.Empty;
+    public int JobApplicationId { get; set; }
+    public JobApplication? JobApplication { get; set; }
+    // "candidate-fit" | "focus-plan"
+    public string NoteType { get; set; } = string.Empty;
+    public string AttachmentContextSignature { get; set; } = string.Empty;
+    public string ResultJson { get; set; } = string.Empty;
+    public DateTimeOffset GeneratedAtUtc { get; set; } = DateTimeOffset.UtcNow;
+}