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_api.go

@@ -0,0 +1,155 @@
+package repository
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"log/slog"
+	"net/http"
+	"regexp"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/spf13/viper"
+
+	"git.kplus.net.ua/yevhen/resource-scraper/types/constant"
+	"git.kplus.net.ua/yevhen/resource-scraper/types/resource"
+)
+
+// srrdbPageSegment locates the page:N segment so a run can continue from N into
+// the following pages.
+var srrdbPageSegment = regexp.MustCompile(`page:(\d+)`)
+
+// srrdbCollectAll walks every page before anything is written, so the caller
+// only ever receives a complete set or an error.
+func srrdbCollectAll(uri string) (*resource.SrrdbSearchResponse, error) {
+	endpoint := strings.TrimRight(viper.GetString("srrdb.endpoint"), "/")
+
+	// The flag binds to its own key and wins over the config value; an unused
+	// flag yields zero.
+	sleep := viper.GetDuration(constant.FlagSleep)
+	if sleep <= 0 {
+		sleep = viper.GetDuration("srrdb.sleep")
+	}
+	if sleep <= 0 {
+		sleep = 2 * time.Second
+	}
+
+	slog.Info("srrdb pacing", "uri", uri, "sleep", sleep)
+
+	page, paginated := srrdbStartPage(uri)
+	collected := &resource.SrrdbSearchResponse{}
+
+	for {
+		url := endpoint + "/" + srrdbWithPage(uri, page, paginated)
+
+		response, err := srrdbFetch(url)
+		if err != nil {
+			return nil, err
+		}
+
+		srrdbCollect(collected, response)
+
+		slog.Info("srrdb page fetched",
+			"url", url,
+			"page", page,
+			"fetched", len(response.Results),
+			"reported", response.ResultsCount)
+
+		if !paginated || len(response.Results) == 0 {
+			break
+		}
+
+		// Everything the API reported is already collected: one more page would
+		// cost a request and a pause to receive an empty answer.
+		if collected.ResultsCount > 0 && len(collected.Results) >= collected.ResultsCount {
+			break
+		}
+
+		page++
+
+		time.Sleep(sleep)
+	}
+
+	return collected, nil
+}
+
+// srrdbCollect merges one page into the answer kept for the dump: results are
+// appended, while resultsCount and query come from the first page.
+func srrdbCollect(all, page *resource.SrrdbSearchResponse) {
+	if all.ResultsCount == 0 {
+		all.ResultsCount = page.ResultsCount
+	}
+
+	if len(all.Query) == 0 {
+		all.Query = page.Query
+	}
+
+	all.Results = append(all.Results, page.Results...)
+	all.Warnings = append(all.Warnings, page.Warnings...)
+}
+
+// srrdbStartPage reads the page:N segment. Without it the path is a single
+// request and no further pages are attempted.
+func srrdbStartPage(uri string) (int, bool) {
+	match := srrdbPageSegment.FindStringSubmatch(uri)
+	if match == nil {
+		return 1, false
+	}
+
+	page, err := strconv.Atoi(match[1])
+	if err != nil || page < 1 {
+		return 1, true
+	}
+
+	return page, true
+}
+
+// srrdbWithPage swaps the page:N segment for the page requested now.
+func srrdbWithPage(uri string, page int, paginated bool) string {
+	if !paginated {
+		return uri
+	}
+
+	return srrdbPageSegment.ReplaceAllString(uri, "page:"+strconv.Itoa(page))
+}
+
+// srrdbFetch performs one search request and decodes the JSON answer.
+func srrdbFetch(url string) (*resource.SrrdbSearchResponse, error) {
+	client := &http.Client{Timeout: 30 * time.Second}
+
+	request, err := http.NewRequest(http.MethodGet, url, nil)
+	if err != nil {
+		return nil, fmt.Errorf("build srrdb request %q: %w", url, err)
+	}
+
+	request.Header.Set("Accept", "application/json")
+
+	response, err := client.Do(request)
+	if err != nil {
+		return nil, fmt.Errorf("request srrdb %q: %w", url, err)
+	}
+
+	defer func() {
+		if cerr := response.Body.Close(); cerr != nil {
+			slog.Error("closing srrdb response body", "url", url, "err", cerr)
+		}
+	}()
+
+	if response.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("srrdb %q replied %s", url, response.Status)
+	}
+
+	body, err := io.ReadAll(io.LimitReader(response.Body, 16<<20))
+	if err != nil {
+		return nil, fmt.Errorf("read srrdb body %q: %w", url, err)
+	}
+
+	decoded := &resource.SrrdbSearchResponse{}
+	if err := json.Unmarshal(body, decoded); err != nil {
+		return nil, fmt.Errorf("decode srrdb body %q: %w", url, err)
+	}
+
+	return decoded, nil
+}