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/cmd/runner/main.go

@@ -152,6 +152,7 @@ func run() error {
 		OrchestratorWorkers:         workers,
 		MetricsAddr:                 cfg.Runner.MetricsAddr,
 		CatalogueRefreshInterval:    cfg.Runner.CatalogueRefreshInterval,
+		CatalogueRequestDelay:       cfg.Runner.CatalogueRequestDelay,
 		SkipInitialCatalogueRefresh: cfg.Runner.SkipInitialCatalogueRefresh,
 		RedisAddr:                   cfg.Redis.Addr,
 		RedisPassword:               cfg.Redis.Password,