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/InterviewPrepNote.cs

@@ -0,0 +1,22 @@
+namespace JobTrackerApi.Models;
+
+// Persists interview prep so it survives tab switches and page reloads instead of being an AI
+// call re-run every time the tab opens (career-workspace-implementation-roadmap.md Phase F5 --
+// "persist interview prep / fit outputs" -- flagged in the product teardown as work evaporating
+// on every re-open). One row per job application; regenerated when the selected attachment
+// context changes or the user explicitly requests a refresh.
+public sealed class InterviewPrepNote
+{
+    public int Id { get; set; }
+    public string OwnerUserId { get; set; } = string.Empty;
+    public int JobApplicationId { get; set; }
+    public JobApplication? JobApplication { get; set; }
+    // Fingerprint of the attachment selection this note was generated from, so a different
+    // attachment selection triggers regeneration without needing an explicit refresh.
+    public string AttachmentContextSignature { get; set; } = string.Empty;
+    public string Summary { get; set; } = string.Empty;
+    public string TalkingPointsJson { get; set; } = "[]";
+    public string LikelyQuestionsJson { get; set; } = "[]";
+    public string WeakSpotsJson { get; set; } = "[]";
+    public DateTimeOffset GeneratedAtUtc { get; set; } = DateTimeOffset.UtcNow;
+}