feat(workspace): interview and follow-up workflow

Phase 5.5. Completes the lifecycle after submission: prepare, communicate, chase.

Interview preparation gets a durable, user-owned store. There were already two
per-application AI stores, InterviewPrepNote and AiWorkspaceNote, but both are
caches that regenerate when their context signature changes — anything a user
typed into them would eventually be overwritten. InterviewPrepItem is the side
nothing regenerates, covering company research, technical notes, behavioural
answers, STAR examples and the user's own questions in one table, because those
categories differ only by label and adding one must not need a migration. Each
item records whether the user wrote it or accepted a suggestion, and an
IsPrepared flag makes the section double as the preparation checklist.

Generation stays in the existing AiWorkspaceService "interview" module, appended
to AiInteraction as before. A suggestion is history until the user adds it as a
prep item; opening the section generates nothing.

Follow-up reuses what exists rather than adding a tracker. The date is
JobApplication.FollowUpAt, the same field RulesEngine and the reminder hosted
service already act on, so reminders keep working with no new wiring. The task
stays an ApplicationChecklistItem in the follow-up category — the section counts
open tasks without owning them. The record is a FollowUpSet JobEvent, the same
type the rest of the app emits.

Communication is untouched: Correspondence already owns recruiter contacts,
history and notes, and the workspace already mounted it.

The timeline interpreter learned five more types — InterviewScheduled,
InterviewCompleted and OfferReceived as milestones, FollowUpCreated and
FollowUpCompleted as routine, deliberately outside the milestone spine so it
stays a summary of what actually happened. JobEvent remains the history source.

InterviewPrepItems is reconciler-owned with a no-op migration, guarded on
JobApplications, and verified on a fresh MariaDB 11: int AUTO_INCREMENT primary
key, varchar owner and title, tinyint flag, datetime(6), composite index inside
the key limit.

371 backend tests, 128 frontend tests, Release build and the production build all
pass locally.

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

JobTrackerApi/Services/StartupInitializationExtensions.cs

@@ -1063,6 +1063,28 @@ public static class StartupInitializationExtensions
                     Exec(c, """CREATE INDEX IF NOT EXISTS "IX_CoverLetterVersions_Owner_Job_Version" ON "CoverLetterVersions" ("OwnerUserId", "JobApplicationId", "Version");""");
                 }
 
+                // Phase 5.5: user-owned interview preparation (not the AI cache InterviewPrepNote).
+                static void EnsureInterviewPrepItemsTable(DbConnection c)
+                {
+                    Exec(c, """
+        CREATE TABLE IF NOT EXISTS "InterviewPrepItems" (
+            "Id" INTEGER NOT NULL CONSTRAINT "PK_InterviewPrepItems" PRIMARY KEY AUTOINCREMENT,
+            "OwnerUserId" TEXT NOT NULL,
+            "JobApplicationId" INTEGER NOT NULL,
+            "Category" TEXT NOT NULL,
+            "Title" TEXT NOT NULL,
+            "Content" TEXT NULL,
+            "Source" TEXT NOT NULL,
+            "IsPrepared" INTEGER NOT NULL,
+            "SortOrder" INTEGER NOT NULL,
+            "CreatedAtUtc" TEXT NOT NULL,
+            "UpdatedAtUtc" TEXT NOT NULL,
+            CONSTRAINT "FK_InterviewPrepItems_JobApplications_JobApplicationId" FOREIGN KEY ("JobApplicationId") REFERENCES "JobApplications" ("Id") ON DELETE CASCADE
+        );
+        """);
+                    Exec(c, """CREATE INDEX IF NOT EXISTS "IX_InterviewPrepItems_Owner_Job_Sort" ON "InterviewPrepItems" ("OwnerUserId", "JobApplicationId", "SortOrder");""");
+                }
+
                 EnsureGmailConnectionsTable(conn);
                 EnsureMicrosoftGraphConnectionsTable(conn);
                 EnsureImapConnectionsTable(conn);
@@ -1077,6 +1099,7 @@ public static class StartupInitializationExtensions
                 EnsureAiInteractionsTable(conn);
                 EnsureApplicationChecklistTable(conn);
                 EnsureCoverLetterVersionsTable(conn);
+                EnsureInterviewPrepItemsTable(conn);
 
                 // Legacy DB signature: migration history exists (AddCorrespondence applied), but 20260310195000 not recorded,
                 // and at least one of the new columns already exists.
@@ -1672,6 +1695,7 @@ public static class StartupInitializationExtensions
                     DropMalformedMySqlTable(conn, "AiInteractions", "CreatedAtUtc", "datetime");
                     DropMalformedMySqlTable(conn, "ApplicationChecklistItems", "CreatedAtUtc", "datetime");
                     DropMalformedMySqlTable(conn, "CoverLetterVersions", "CreatedAtUtc", "datetime");
+                    DropMalformedMySqlTable(conn, "InterviewPrepItems", "CreatedAtUtc", "datetime");
 
                     if (!HasMySqlTable(conn, "CvVariants") && HasMySqlTable(conn, "JobApplications"))
                     {
@@ -1773,6 +1797,30 @@ public static class StartupInitializationExtensions
                         cmd.ExecuteNonQuery();
                     }
 
+                    if (!HasMySqlTable(conn, "InterviewPrepItems") && HasMySqlTable(conn, "JobApplications"))
+                    {
+                        using var cmd = conn.CreateCommand();
+                        cmd.CommandText = @"CREATE TABLE IF NOT EXISTS `InterviewPrepItems` (
+        `Id` int NOT NULL AUTO_INCREMENT,
+        `OwnerUserId` varchar(255) NOT NULL,
+        `JobApplicationId` int NOT NULL,
+        `Category` varchar(32) NOT NULL,
+        `Title` varchar(500) NOT NULL,
+        `Content` longtext NULL,
+        `Source` varchar(16) NOT NULL,
+        `IsPrepared` tinyint(1) NOT NULL,
+        `SortOrder` int NOT NULL,
+        `CreatedAtUtc` datetime(6) NOT NULL,
+        `UpdatedAtUtc` datetime(6) NOT NULL,
+        PRIMARY KEY (`Id`),
+        CONSTRAINT `FK_InterviewPrepItems_JobApplications_JobApplicationId` FOREIGN KEY (`JobApplicationId`) REFERENCES `JobApplications` (`Id`) ON DELETE CASCADE
+        );";
+                        cmd.ExecuteNonQuery();
+                    }
+
+                    EnsureMySqlAutoIncrementPrimaryKey(conn, "InterviewPrepItems", "Id");
+                    EnsureMySqlIndex(conn, "InterviewPrepItems", "IX_InterviewPrepItems_Owner_Job_Sort", "`OwnerUserId`, `JobApplicationId`, `SortOrder`");
+
                     EnsureMySqlAutoIncrementPrimaryKey(conn, "CoverLetterVersions", "Id");
                     EnsureMySqlIndex(conn, "CoverLetterVersions", "IX_CoverLetterVersions_Owner_Job_Version", "`OwnerUserId`, `JobApplicationId`, `Version`");