fix(runner): harden catalogue scrape against 429s; disable sourcemap upload

- scraper.go: ScrapeCatalogue now uses retryGet (9 attempts, 10s base) +
  500–1500ms inter-page jitter instead of bare GetContent. ScrapeMetadata
  also switched to retryGet so a single 429 on a book page is retried rather
  than aborting the whole refresh.
- catalogue_refresh.go: per-book delay is now configurable
  (RUNNER_CATALOGUE_REQUEST_DELAY, default 2s) + up to 50% random jitter
  applied before every metadata fetch. Only metadata is scraped here —
  chapters are fetched on-demand, not during catalogue refresh. Progress
  logged every 50 books instead of 100.
- config.go / runner.go / main.go: add CatalogueRequestDelay field wired
  from RUNNER_CATALOGUE_REQUEST_DELAY env var.
- release.yaml: comment out upload-sourcemaps job and remove it from the
  release needs; GlitchTip auth token needs refreshing after DB wipe.

backend/internal/runner/runner.go

@@ -62,6 +62,10 @@ type Config struct {
 	// scrapes per-book metadata, downloads covers, and re-indexes everything in
 	// Meilisearch. Defaults to 24h (expensive — full catalogue walk).
 	CatalogueRefreshInterval time.Duration
+	// CatalogueRequestDelay is the base inter-request pause during a catalogue
+	// refresh metadata walk. Jitter of up to 50% is added on top.
+	// Defaults to 2s. Set via RUNNER_CATALOGUE_REQUEST_DELAY.
+	CatalogueRequestDelay time.Duration
 	// SkipInitialCatalogueRefresh suppresses the immediate catalogue walk that
 	// otherwise fires at startup. The periodic ticker (CatalogueRefreshInterval)
 	// still fires normally. Set RUNNER_SKIP_INITIAL_CATALOGUE_REFRESH=true for
@@ -145,6 +149,9 @@ func New(cfg Config, deps Dependencies) *Runner {
 	if cfg.CatalogueRefreshInterval <= 0 {
 		cfg.CatalogueRefreshInterval = 24 * time.Hour
 	}
+	if cfg.CatalogueRequestDelay <= 0 {
+		cfg.CatalogueRequestDelay = 2 * time.Second
+	}
 	if cfg.MetricsAddr == "" {
 		cfg.MetricsAddr = ":9091"
 	}