feat(admin): replace all native confirm() with styled dialog + fix pipeline tabs scrollbar

- Add global htmx:confirm handler in base_admin.html that intercepts
  hx-confirm attributes and shows #confirm-dialog instead of window.confirm()
- Convert 4 pipeline HTMX buttons (Run Transform, Run Export, Run Full
  Pipeline, Run extractor) from onclick+confirm() to hx-confirm
- Convert 4 affiliate form/list delete buttons from onclick+confirm()
  to confirmAction() via event.preventDefault()
- Add scrollbar-width:none + ::-webkit-scrollbar{display:none} to
  .pipeline-tabs to suppress spurious horizontal scrollbar

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CHANGELOG.md

@@ -6,6 +6,10 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 
 ## [Unreleased]
 
+### Changed
+- **Admin: styled confirm dialog for all destructive actions** — replaced all native `window.confirm()` calls with the existing `#confirm-dialog` styled `<dialog>`. A new global `htmx:confirm` handler intercepts HTMX confirmation prompts and shows the dialog; form-submit buttons on affiliate pages were updated to use `confirmAction()`. Affected: pipeline Transform tab (Run Transform, Run Export, Run Full Pipeline), pipeline Overview tab (Run extractor), affiliate product delete, affiliate program delete (both form and list variants).
+- **Pipeline tabs: no scrollbar** — added `scrollbar-width: none` and `::-webkit-scrollbar { display: none }` to `.pipeline-tabs` to suppress the spurious horizontal scrollbar on narrow viewports.
+
 ### Fixed
 - **Stale-tier failures no longer exhaust the next proxy tier** — with parallel workers, threads that fetched a proxy just before tier escalation reported failures after the tier changed, immediately blowing through the new tier's circuit breaker before it ever got tried (Rayobyte was skipped entirely). `record_failure(proxy_url)` now checks which tier the proxy belongs to and ignores the circuit breaker when the proxy is from an already-escalated tier.