fix(jobs): derive attachment checklist flags from actual Attachments

Backlog item 4 (Wave 3, first sub-item). HasResume/HasCoverLetter/HasPortfolio/
HasOtherAttachment were manually-editable checkboxes in EditJobDialog,
completely independent of whether a file was actually attached -- classic
drift: mark 'resume ready' by hand, later delete the resume attachment, flag
stays stuck true forever. User confirmed (asked directly, since removing the
manual-override capability is a product decision, not purely technical):
make them fully computed from Attachments, no manual override.

- AttachmentsController.RecomputeAttachmentFlagsAsync: the single place these
  four fields get written now, called after every attachment mutation
  (upload, delete, Purpose change) that could affect them. Deliberately kept
  as persisted columns (not [NotMapped] computed properties reading the
  Attachments navigation collection) -- ~15 query sites build JobApplication
  DTOs without .Include(Attachments), so a live-computed property would
  silently return false everywhere instead of throwing, the worst kind of
  bug. Recomputing at the one write funnel avoids touching any read path.
- Removed HasResume/etc from CreateJobApplicationRequest/
  UpdateJobApplicationRequest -- no longer client-settable.
- EditJobDialog: removed the manual checkboxes, kept the (now genuinely
  accurate) read-only status chips.
- AddJobModal: stopped sending has*-flags at job-creation time; the
  follow-up attachment upload call now sets them correctly via the same
  recompute path.

Caught a real bug while testing this: the Purpose-change path recomputed
before saving the Purpose change, so a fresh query missed the pending edit
and the flags never updated. Fixed by committing the mutation before
recomputing.

3 new backend tests (purpose-change sets flag, delete clears flag,
non-primary purpose counts as "other"). 172/172 backend, 25/25 frontend
suites (57 tests) green.

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

JobTrackerApi/Controllers/AttachmentsController.cs

@@ -59,6 +59,26 @@ namespace JobTrackerApi.Controllers
             return "other";
         }
 
+        // JobApplication.HasResume/HasCoverLetter/HasPortfolio/HasOtherAttachment are derived
+        // from actual Attachment rows, not manually settable -- this is the single place they're
+        // written, called after every attachment mutation (upload/delete/purpose change) so they
+        // can never drift from what's actually attached.
+        private async Task RecomputeAttachmentFlagsAsync(int jobId, CancellationToken cancellationToken)
+        {
+            var job = await _db.JobApplications.FirstOrDefaultAsync(j => j.Id == jobId, cancellationToken);
+            if (job is null) return;
+
+            var purposes = await _db.Attachments
+                .Where(a => a.JobApplicationId == jobId)
+                .Select(a => a.Purpose)
+                .ToListAsync(cancellationToken);
+
+            job.HasResume = purposes.Any(p => p == "resume");
+            job.HasCoverLetter = purposes.Any(p => p == "cover-letter");
+            job.HasPortfolio = purposes.Any(p => p == "portfolio");
+            job.HasOtherAttachment = purposes.Any(p => p is not ("resume" or "cover-letter" or "portfolio"));
+        }
+
         [HttpGet("{jobId:int}")]
         public async Task<ActionResult<List<AttachmentDto>>> ListForJob([FromRoute] int jobId, CancellationToken cancellationToken)
         {
@@ -102,15 +122,23 @@ namespace JobTrackerApi.Controllers
                 att.UseForAi = request.UseForAi.Value;
             }
 
-            if (!string.IsNullOrWhiteSpace(request.Purpose))
+            var purposeChanged = !string.IsNullOrWhiteSpace(request.Purpose);
+            if (purposeChanged)
             {
-                att.Purpose = request.Purpose.Trim().ToLowerInvariant();
+                att.Purpose = request.Purpose!.Trim().ToLowerInvariant();
             }
 
             var rawName = (request.FileName ?? string.Empty).Trim();
             if (rawName.Length == 0)
             {
                 await _db.SaveChangesAsync(cancellationToken);
+                if (purposeChanged)
+                {
+                    // Recompute needs the Purpose change committed first -- a fresh query
+                    // wouldn't see the pending change yet.
+                    await RecomputeAttachmentFlagsAsync(att.JobApplicationId, cancellationToken);
+                    await _db.SaveChangesAsync(cancellationToken);
+                }
                 return NoContent();
             }
 
@@ -130,6 +158,11 @@ namespace JobTrackerApi.Controllers
             att.FileName = name;
             att.FilePath = newPath;
             await _db.SaveChangesAsync(cancellationToken);
+            if (purposeChanged)
+            {
+                await RecomputeAttachmentFlagsAsync(att.JobApplicationId, cancellationToken);
+                await _db.SaveChangesAsync(cancellationToken);
+            }
 
             return NoContent();
         }
@@ -141,8 +174,11 @@ namespace JobTrackerApi.Controllers
             if (att is null) return NotFound();
 
             var path = att.FilePath;
+            var jobId = att.JobApplicationId;
             _db.Attachments.Remove(att);
             await _db.SaveChangesAsync(cancellationToken);
+            await RecomputeAttachmentFlagsAsync(jobId, cancellationToken);
+            await _db.SaveChangesAsync(cancellationToken);
 
             try
             {
@@ -200,6 +236,8 @@ namespace JobTrackerApi.Controllers
                 });
             }
 
+            await _db.SaveChangesAsync(cancellationToken);
+            await RecomputeAttachmentFlagsAsync(jobId, cancellationToken);
             await _db.SaveChangesAsync(cancellationToken);
             return Ok();
         }