srrdb: harvest the srrDB search API into a separate SQLite database

New scope reading the API instead of scraping HTML: one search path per run,
passed raw through --single-uri, and the answer stored as-is into its own
SQLite file created from the embedded schema.

Command line: --single-uri carries the path after /v1/search/
(category:flac/date:today/page:1) and must name a category; --sleep sets the
pause between pages, with the config value as fallback. A day named on the
command line is always fetched again and its dump rewritten, so cron can
refresh today hourly and yesterday daily.

Date placeholders: date:auto walks backwards to the newest day in
[srrdb.floor..yesterday] that has no dump yet, closing holes instead of
declaring the archive covered. date:today, date:yesterday and date:tomorrow
stand for the neighbouring days. Today is never taken by the walk, because a
day still being filled would be frozen by its own dump after the first run.

Dumps are the cursor as well as the record, so a missing dump directory is an
error instead of "nothing harvested yet": a renamed, unmounted or mistyped
directory must not send the run silently back to the beginning. An empty day is
a normal result and is remembered as harvested; API warnings never are, and
they reach the exit code.

Writes go through one transaction, so a day lands completely or not at all.
group and category come from the release line and the search path; status, nfo,
content and synced_at stay NULL. srrdb.log.jsonl records one line per finished
run, srrdb.error_log.jsonl keeps failures and API warnings apart by a kind
field.

Also: the console command contract returns (string, error), so a failing scope
reaches the process exit code and cron can tell a failed run from a successful
one. config/scope/srrdb.yaml is untracked because its paths differ per host.
modernc.org/sqlite replaces the archived libsql client, which only ever talked
to a server. pkg/repository/srrdb.go is split by responsibility and covered by
table-driven tests.

pkg/repository/srrdb_dump.go

@@ -0,0 +1,62 @@
+package repository
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io/fs"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"github.com/spf13/viper"
+
+	"git.kplus.net.ua/yevhen/resource-scraper/types/resource"
+)
+
+// srrdbNormalizedPath turns a search path into a file name. The two characters
+// that carry structure in a path are swapped for look-alikes, so the name still
+// reads as the query it came from and can be reversed character by character.
+func srrdbNormalizedPath(uri string) string {
+	return strings.NewReplacer(":", "：", "/", "∕").Replace(uri) + ".json"
+}
+
+// srrdbDumpPath is the guard file of a search path inside srrdb.dump_dir.
+func srrdbDumpPath(uri string) string {
+	return filepath.Join(viper.GetString("srrdb.dump_dir"), srrdbNormalizedPath(uri))
+}
+
+// srrdbExists reports whether a dump file is present. Any stat failure other than
+// "not found" is returned as an error: treating it as absent would let the run
+// overwrite a dump it has no right to read.
+func srrdbExists(path string) (bool, error) {
+	_, err := os.Stat(path)
+
+	switch {
+	case err == nil:
+		return true, nil
+	case errors.Is(err, fs.ErrNotExist):
+		return false, nil
+	default:
+		return false, fmt.Errorf("stat srrdb dump %q: %w", path, err)
+	}
+}
+
+// srrdbWriteDump stores the merged answer as indented JSON. It runs only after
+// the database is updated, therefore the presence of the file means the whole
+// run completed.
+//
+// The directory is never created here: it holds the cursor of the walk and is made
+// once by hand, like the database file.
+func srrdbWriteDump(path string, all *resource.SrrdbSearchResponse) error {
+	data, err := json.MarshalIndent(all, "", "  ")
+	if err != nil {
+		return fmt.Errorf("encode srrdb dump %q: %w", path, err)
+	}
+
+	if err := os.WriteFile(path, data, 0o644); err != nil {
+		return fmt.Errorf("write srrdb dump %q: %w", path, err)
+	}
+
+	return nil
+}