Made the fetcher save what it fetches, with fetcher.WithStore

With WithStore, the Find a Tender and mock workers save each run's
opportunities with SaveOpportunities and log what changed; a failed save
fails the run, so the checkpoint stays put and the next run retries.
Without a store nothing is persisted. The mock's opportunities are saved
with Source "FTSMock" rather than the converter's "FindATender".

fetcher service and job-search serve open the store at database.file
(cli.OpenConfiguredStore), or warn and run without one. A missing file
isn't created, and a database needing migration says to run job-search
migrate.

Fixed upsertOpportunity, which never wrote the source column, so every
saved opportunity had an empty Source.

internal/cli/fetch/service.go

@@ -2,6 +2,7 @@ package fetch
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"log/slog"
 	"os"
@@ -25,7 +26,7 @@ func commandService(opts *cli.Options) *cobra.Command {
 		PersistentPostRun: func(cmd *cobra.Command, args []string) {
 			slog.Debug("command persistent post-run", "command", "service")
 		},
-		RunE: func(cmd *cobra.Command, args []string) error {
+		RunE: func(cmd *cobra.Command, args []string) (err error) {
 			slog.Debug("command run", "command", "service")
 
 			foreground, _ := cmd.Flags().GetBool("foreground")
@@ -53,7 +54,23 @@ func commandService(opts *cli.Options) *cobra.Command {
 				stop()
 			}()
 
-			return fetcher.New(&conf.Sources).Run(ctx, since)
+			var fetcherOptions []fetcher.Option
+			opportunityStore, openErr := cli.OpenConfiguredStore(ctx, conf)
+			switch {
+			case errors.Is(openErr, cli.ErrNoDatabase):
+				slog.Warn("not storing fetched opportunities", "reason", openErr)
+			case openErr != nil:
+				return openErr
+			default:
+				defer func() {
+					err = errors.Join(err, opportunityStore.Close())
+				}()
+				fetcherOptions = append(
+					fetcherOptions, fetcher.WithStore(opportunityStore),
+				)
+			}
+
+			return fetcher.New(&conf.Sources, fetcherOptions...).Run(ctx, since)
 		},
 	}
 	cmd.Flags().Time(