feat(db): add source column to relationships table (#44)

Promote BOM source from metadata JSONB to a dedicated VARCHAR(20)
column with CHECK constraint ('manual' or 'assembly').

- Add migration 012_bom_source.sql (column, data migration, cleanup)
- Add Source field to Relationship and BOMEntry structs
- Update all SQL queries (GetBOM, GetWhereUsed, GetExpandedBOM, Create)
- Update API response/request types with source field
- Update CSV/ODS export to read e.Source instead of metadata
- Update CSV import to set source on relationship directly
- Update frontend types and BOMTab to use top-level source field

internal/api/bom_handlers.go

@@ -29,6 +29,7 @@ type BOMEntryResponse struct {
 	ChildRevision        *int           `json:"child_revision,omitempty"`
 	EffectiveRevision    int            `json:"effective_revision"`
 	Depth                *int           `json:"depth,omitempty"`
+	Source               string         `json:"source"`
 	Metadata             map[string]any `json:"metadata,omitempty"`
 }
 
@@ -51,6 +52,7 @@ type AddBOMEntryRequest struct {
 	Unit                 *string        `json:"unit,omitempty"`
 	ReferenceDesignators []string       `json:"reference_designators,omitempty"`
 	ChildRevision        *int           `json:"child_revision,omitempty"`
+	Source               string         `json:"source,omitempty"`
 	Metadata             map[string]any `json:"metadata,omitempty"`
 }
 
@@ -240,6 +242,7 @@ func (s *Server) HandleAddBOMEntry(w http.ResponseWriter, r *http.Request) {
 		Unit:                 req.Unit,
 		ReferenceDesignators: req.ReferenceDesignators,
 		ChildRevision:        req.ChildRevision,
+		Source:               req.Source,
 		Metadata:             req.Metadata,
 	}
 	if user := auth.UserFromContext(ctx); user != nil {
@@ -273,6 +276,7 @@ func (s *Server) HandleAddBOMEntry(w http.ResponseWriter, r *http.Request) {
 		ReferenceDesignators: req.ReferenceDesignators,
 		ChildRevision:        req.ChildRevision,
 		EffectiveRevision:    child.CurrentRevision,
+		Source:               rel.Source,
 		Metadata:             req.Metadata,
 	}
 	if req.ChildRevision != nil {
@@ -434,6 +438,7 @@ func bomEntryToResponse(e *db.BOMEntry) BOMEntryResponse {
 		ReferenceDesignators: refDes,
 		ChildRevision:        e.ChildRevision,
 		EffectiveRevision:    e.EffectiveRevision,
+		Source:               e.Source,
 		Metadata:             e.Metadata,
 	}
 }
@@ -686,14 +691,14 @@ func (s *Server) HandleExportBOMCSV(w http.ResponseWriter, r *http.Request) {
 		}
 
 		row := []string{
-			strconv.Itoa(i + 1),                             // Item
-			strconv.Itoa(e.Depth),                           // Level
-			getMetaString(e.Metadata, "source"),             // Source
-			e.ChildPartNumber,                               // PN
+			strconv.Itoa(i + 1),   // Item
+			strconv.Itoa(e.Depth), // Level
+			e.Source,              // Source
+			e.ChildPartNumber,     // PN
 			getMetaString(e.Metadata, "seller_description"), // Seller Description
-			unitCostStr,                                     // Unit Cost
-			qtyStr,                                          // QTY
-			extCost,                                         // Ext Cost
+			unitCostStr, // Unit Cost
+			qtyStr,      // QTY
+			extCost,     // Ext Cost
 			getMetaString(e.Metadata, "sourcing_link"), // Sourcing Link
 		}
 		if err := writer.Write(row); err != nil {
@@ -853,12 +858,11 @@ func (s *Server) HandleImportBOMCSV(w http.ResponseWriter, r *http.Request) {
 		}
 
 		// Build metadata from CSV columns
-		metadata := make(map[string]any)
+		source := ""
 		if idx, ok := headerIdx["source"]; ok && idx < len(record) {
-			if v := strings.TrimSpace(record[idx]); v != "" {
-				metadata["source"] = v
-			}
+			source = strings.TrimSpace(record[idx])
 		}
+		metadata := make(map[string]any)
 		if idx, ok := headerIdx["seller description"]; ok && idx < len(record) {
 			if v := strings.TrimSpace(record[idx]); v != "" {
 				metadata["seller_description"] = v
@@ -942,6 +946,7 @@ func (s *Server) HandleImportBOMCSV(w http.ResponseWriter, r *http.Request) {
 				ChildItemID:  child.ID,
 				RelType:      "component",
 				Quantity:     quantity,
+				Source:       source,
 				Metadata:     metadata,
 				CreatedBy:    importUsername,
 			}

internal/api/ods.go

@@ -599,7 +599,7 @@ func (s *Server) HandleExportBOMODS(w http.ResponseWriter, r *http.Request) {
 			}
 		}
 
-		source := getMetaString(e.Metadata, "source")
+		source := e.Source
 		if source == "" && childItem != nil {
 			st := childItem.SourcingType
 			if st == "manufactured" {
@@ -754,7 +754,7 @@ func (s *Server) HandleProjectSheetODS(w http.ResponseWriter, r *http.Request) {
 				if e.Quantity != nil {
 					qty = *e.Quantity
 				}
-				source := getMetaString(e.Metadata, "source")
+				source := e.Source
 				if source == "" && childItem != nil {
 					if childItem.SourcingType == "manufactured" {
 						source = "M"