[WIP] Improve blocking pattern detection in submit mode

[yyq1043-cloud]

Summary

Expand Cloudflare and anti-bot detection in the submit mode ("check_features_manually") to catch more blocking patterns with clearer error messages.

Before:
Only detected /cdn-cgi/challenge-platform, now: pattern, and "Sorry, you have been blocked".

After:
Detects 6 common blocking patterns:

• Cloudflare challenge platform
• Cloudflare turnstile ("Now checking your browser")
• Cloudflare general blocks
• Generic "blocked" pages
• Access denied pages
• Cloudflare-specific header presence

Example improvement:
When a Cloudflare turnstile is detected, the user now sees:

Cloudflare turnstile detected, skipping

instead of the generic message.

Closes #2668 (partial: addresses the "filter by errors" TODO)

[yyq1043-cloud]

Hi! I'd like to request review for this PR: Improve blocking pattern detection in submit mode
Requesting review from: @soxoj
Thank you! 🙂

[soxoj]

Thanks for the PR! A few blockers before this can be merged:

1. Scope mismatch. Title and Complete --submit mode: urlProbe, activation, cookies, status_codes, update-existing #2668 say "submit mode blocking detection", but 2 of 3 files (simple_report.tpl, simple_report_pdf.tpl) add web.archive.org / archive.is links to HTML/PDF reports — unrelated. Please split into two PRs.

2. Wrong pattern. "CF-Chl-Alg-List:" is an HTTP header name, but first_html_response is the response body — headers won't appear there, so this check never fires. Also, "Now checking your browser" is labeled "Cloudflare turnstile", but that string is the old interstitial challenge page; Turnstile is a widget with different markers.

3. Silent regression. The original "\t\t\t\tnow: " pattern is dropped without explanation — please keep it or justify removal.

4. No tests for the new patterns.

5. English-only markers. Many sites in maigret are non-English; consider whether matching only English strings is enough, or if these need locale-agnostic signals.

[yyq1043-cloud]

Hi! I'd like to request review for this PR: [WIP] Improve blocking pattern detection in submit mode
Requesting review from: @soxoj
Thank you! 🙂