feat: resolve drawing revisions on PDF upload

When a PDF hash is set on an export record, resolve or create the
associated Drawing and bump its revision if the content hash changed.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

FabWorks.Api/Controllers/ExportsController.cs

@@ -212,11 +212,50 @@ namespace FabWorks.Api.Controllers
             if (record == null) return NotFound();
 
             record.PdfContentHash = request.PdfContentHash;
+
+            if (!string.IsNullOrEmpty(record.DrawingNumber) && !string.IsNullOrEmpty(request.PdfContentHash))
+            {
+                var drawing = await ResolveDrawingAsync(record.DrawingNumber, record.Title, request.PdfContentHash);
+                record.DrawingId = drawing.Id;
+            }
+
             await _db.SaveChangesAsync();
 
             return NoContent();
         }
 
+        private async Task<Drawing> ResolveDrawingAsync(string drawingNumber, string title, string pdfContentHash)
+        {
+            var drawing = await _db.Drawings
+                .FirstOrDefaultAsync(d => d.DrawingNumber == drawingNumber);
+
+            if (drawing == null)
+            {
+                drawing = new Drawing
+                {
+                    DrawingNumber = drawingNumber,
+                    Title = title,
+                    PdfContentHash = pdfContentHash,
+                    Revision = 1
+                };
+                _db.Drawings.Add(drawing);
+            }
+            else if (drawing.PdfContentHash != pdfContentHash)
+            {
+                drawing.PdfContentHash = pdfContentHash;
+                drawing.Revision++;
+                if (!string.IsNullOrEmpty(title))
+                    drawing.Title = title;
+            }
+            // If hash matches, keep same revision (just update title if needed)
+            else if (!string.IsNullOrEmpty(title))
+            {
+                drawing.Title = title;
+            }
+
+            return drawing;
+        }
+
         [HttpGet("previous-cut-template")]
         public async Task<ActionResult<CutTemplateDto>> GetPreviousCutTemplate(
             [FromQuery] string drawingNumber,