Split fetch from jobsearch into a separate fetcher command, and renamed fetch once to fts-once

job-search no longer has a fetch command. Its subcommands are now in
cmd/fetcher, which reads the same configuration: "fetcher service" runs
every enabled source's fetcher on its interval until stopped, and
"fetcher fts-once" (was "fetch once") fetches from Find a Tender once and
prints the releases as JSON. The new namea say what the commands do,
because service runs every source while fts-once fetches only from Find a
Tender.

The code stays in internal/cli/fetch, where NewCommands replaces the fetch
parent command. once.go is now fts_once.go and commandOnce is
commandFTSOnce. The README's usage, the config README and the find_a_tender
api_root comment now give the new command names.

internal/cli/fetch/service.go

@@ -18,15 +18,15 @@ import (
 func commandService(opts *cli.Options) *cobra.Command {
 	cmd := &cobra.Command{
 		Use:   "service",
-		Short: "Fetch current opportunities - background service",
+		Short: "Run every enabled source's fetcher on its interval until stopped",
 		PersistentPreRun: func(cmd *cobra.Command, args []string) {
-			slog.Debug("command persistent pre-run", "command", "fetch.service")
+			slog.Debug("command persistent pre-run", "command", "service")
 		},
 		PersistentPostRun: func(cmd *cobra.Command, args []string) {
-			slog.Debug("command persistent post-run", "command", "fetch.service")
+			slog.Debug("command persistent post-run", "command", "service")
 		},
 		RunE: func(cmd *cobra.Command, args []string) error {
-			slog.Debug("command run", "command", "fetch.service")
+			slog.Debug("command run", "command", "service")
 
 			foreground, _ := cmd.Flags().GetBool("foreground")