Made the fetcher a Fetcher type with per-source config, and ran it in job-search serve

fetcher.Run(ctx, conf, since) becomes New(&conf.Sources, opts...) and
Run(ctx, since). Each worker now takes only its own source's config, and
Run starts each one through a closure that binds it. Cancelling ctx stops
the workers through the Fetcher's background context, and Run always waits
for every worker before returning their joined errors.

The findatender client no longer holds the configuration: New takes only
the API root, ReloadConfig is gone, and request tracing follows
logging.IsDebugEnabled(). The FindAOpportunity worker is now FindATender.

job-search serve runs the fetcher alongside the HTTP server. A source that
fails stops the server, and the server stopping stops the sources; with no
sources enabled the server keeps running. fetcher service and fetcher
fts-once use the new APIs.

internal/fetcher/worker_findatender.go

@@ -12,43 +12,43 @@ import (
 	"git.avsdev.uk/Go/job-search/internal/util"
 )
 
-// runFindAOpportunity polls Find a Tender every configured interval until ctx
+// runFindATender polls Find a Tender every configured interval until ctx
 // is cancelled.
-func runFindAOpportunity(
+func runFindATender(
 	ctx context.Context,
 	logger *slog.Logger,
-	conf *config.JobSearchConfig,
+	conf *config.JSCSourceFindATender,
 	since time.Time,
 ) error {
-	if conf.Sources.FindATender.APIRoot == "" {
+	if conf.APIRoot == "" {
 		return errors.New("fetcher: sources.find_a_tender.api_root is not set")
 	}
 
 	worker := util.Worker{
 		Logger:   tagged(logger),
-		Name:     "FindAOpportunity",
-		Interval: conf.Sources.FindATender.Interval,
+		Name:     "FindATender",
+		Interval: conf.Interval,
 		Task: func(ctx context.Context, since time.Time) error {
-			return fetchFindAOpportunity(ctx, logger, conf, since)
+			return fetchFindATender(ctx, logger, conf, since)
 		},
 	}
 	return worker.Run(ctx, since)
 }
 
-// fetchFindAOpportunity fetches everything updated since since from Find a
+// fetchFindATender fetches everything updated since since from Find a
 // Tender. Finding nothing returns ErrNoNewReleases, so the worker still moves
 // its checkpoint on.
-func fetchFindAOpportunity(
+func fetchFindATender(
 	ctx context.Context,
 	logger *slog.Logger,
-	conf *config.JobSearchConfig,
+	conf *config.JSCSourceFindATender,
 	since time.Time,
 ) error {
 	opportunities, err := util.AwaitTask(
 		ctx,
 		func() ([]*types.Opportunity, error) {
 			findATender := findatender.New(
-				conf, conf.Sources.FindATender.APIRoot, findatender.WithLogger(logger),
+				conf.APIRoot, findatender.WithLogger(logger),
 			)
 			defer findATender.Shutdown()
 			return findATender.With(ctx).FetchAll(since, true)