chore: drop /geo-debug route and ?region= dev override

Both were intended as local QA helpers and shouldn't ship to production.

* /geo-debug exposed an internal matcher diagnostic panel that probes
  the visitor's geo and evaluates a battery of Location matcher rules.
  Useful in dev, but a public production route would leak internal
  framework behaviour to anyone who guesses the URL.
* The outer worker wrapper that read ?region= and rewrote cf-region-code
  let any visitor bypass real geo with a URL parameter — same issue.

Only the cache-segment fix (regionId from cf-region-code in
buildSegment) stays — it's the production-safe piece that makes the
Location matcher cache correctly per region.

src/matchers/location.ts also dropped: it was only consumed by the
removed route. The upstream fix lands via decocms/blocks#209 and
the storefront's @decocms/start bump.

Author: JonasJesus42