Speakers list #134

As a regular attendee,
I want to browse every speaker who has presented at ruby.uy,
so that I can recognize the community and rediscover talks by people I liked.
AC:

• /speakers/ lists every _data/people.yml entry who appears in a meetup's talks
• Per speaker: avatar (GitHub), name, talk count, list of their talk titles linking to the
  meetup anchor
• Sorted alphabetically, total count shown at top ("N speakers en N años")
• Linked from footer
• Dependency: people.yml must be backfilled for any past talks currently missing speaker
  entries (separate sub-ticket)