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/fetcher/worker_ftsmock.go

@@ -12,12 +12,16 @@ import (
 	"git.avsdev.uk/Go/job-search/internal/util"
 )
 
+// ftsMockSource is the Source of the opportunities the mock source fetches.
+const ftsMockSource = "FTSMock"
+
 // runFTSMock polls the mock Find a Tender server every configured interval
-// until ctx is cancelled.
+// until ctx is cancelled, passing what each run fetches to save.
 func runFTSMock(
 	ctx context.Context,
 	logger *slog.Logger,
 	conf *config.JSCSourceFTSMock,
+	save saveFunc,
 	since time.Time,
 ) error {
 	if conf.APIRoot == "" {
@@ -26,24 +30,30 @@ func runFTSMock(
 
 	worker := util.Worker{
 		Logger:   tagged(logger),
-		Name:     "FTSMock",
+		Name:     ftsMockSource,
 		Interval: conf.Interval,
 		Task: func(ctx context.Context, since time.Time) error {
-			return fetchFTSMock(ctx, logger, conf, since)
+			opportunities, err := fetchFTSMock(ctx, logger, conf, since)
+			if err != nil {
+				return err
+			}
+			return save(ctx, logger, opportunities)
 		},
 	}
 	return worker.Run(ctx, since)
 }
 
 // fetchFTSMock fetches everything updated since since from the mock Find a
-// Tender server. Finding nothing returns ErrNoNewReleases, so the worker still
-// moves its checkpoint on.
+// Tender server. The mock serves the real API's format, so the converter
+// marks the opportunities as Find a Tender's; their Source is set to
+// ftsMockSource here instead. Finding nothing returns ErrNoNewReleases, so
+// the worker still moves its checkpoint on.
 func fetchFTSMock(
 	ctx context.Context,
 	logger *slog.Logger,
 	conf *config.JSCSourceFTSMock,
 	since time.Time,
-) error {
+) ([]*types.Opportunity, error) {
 	opportunities, err := util.AwaitTask(
 		ctx,
 		func() ([]*types.Opportunity, error) {
@@ -55,13 +65,17 @@ func fetchFTSMock(
 		},
 	)
 	if errors.Is(err, findatender.ErrNoReleases) {
-		return ErrNoNewReleases
+		return nil, ErrNoNewReleases
 	}
 	if err != nil {
-		return err
+		return nil, err
+	}
+
+	for _, opportunity := range opportunities {
+		opportunity.Source = ftsMockSource
 	}
 
 	tagged(logger).Info("fetched opportunities", "count", len(opportunities))
 
-	return nil
+	return opportunities, nil
 }