Add x.com URL support and update Twitter provider endpoint

[philltran]

Twitter rebranded to X and the primary domain for post URLs is now x.com.
The existing provider only matched twitter.com URLs and proxied to the legacy
publish.twitter.com endpoint, so x.com/... post URLs returned no embed.

Changes (lib/Noembed/Provider/Twitter.pm)

• Pattern: extended to match both twitter.com and x.com post URLs
  (including www., mobile., and #!/ hash-bang variants).
• URL normalization: x.com URLs are rewritten to twitter.com before
  calling the endpoint. publish.x.com/oembed does not reliably handle
  x.com-domain input — this is a documented platform bug with confirmed
  workarounds in WordPress core, Umbraco, Ghost, and Rocket.Chat.
  • Twitter/𝕏 Embeds Fail When Using x.com Domain URLs WordPress/gutenberg#66980
  • Twitter embeds broken now that it is "x.com" umbraco/Umbraco-CMS#16645
  • Twitter/X oembed (link preview) does not work RocketChat/Rocket.Chat#37429
• Endpoint: updated to the canonical https://publish.x.com/oembed
  per X developer documentation (https://docs.x.com/x-for-websites/oembed-api).
• Provider name: updated to X (formerly Twitter).

Testing

# x.com — now matches                                                                                                                                                                                                                
curl "http://localhost:5000/embed?url=https://x.com/<user>/status/<id>"                                                                                                                                                              
# twitter.com — still works                                                                                                                                                                                                          
curl "http://localhost:5000/embed?url=https://twitter.com/<user>/status/<id>"                                                                                                                                                        
# mobile variants                                                                                                                                                                                                                    
curl "http://localhost:5000/embed?url=https://mobile.x.com/<user>/status/<id>"                                                                                                                                                       
curl "http://localhost:5000/embed?url=https://mobile.twitter.com/<user>/status/<id>"                                                                                                                                                 
                                                                                                                                                                                                                                     
Expected: 200 JSON with provider_name: "X (formerly Twitter)" and an html                                                                                                                                                            
field containing a <blockquote> embed.