Read an address typed without a scheme as https (#101)

cnn-com was added as 'cnn.com', stored as typed, and every check failed with "relative URL
without a base" before it reached the site to look for its feed. expand_input, which both the
web page and `ipx add` pass the address through, now makes one without a scheme https, and a
protocol-relative //host/path https too.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CHANGELOG.md

@@ -50,6 +50,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
+- Adding a site without `https://`, such as `cnn.com`, works; it failed on every check.
 - A limit on new downloads per check means a show's newest episodes: with it set to 3, ipx no longer works back through the show's history three at a time. Set to 0, it still takes the whole back catalogue.
 - With no limit on new downloads per check (`max_new_per_check = 0`), downloads work on Postgres; they failed.
 - Checking a feed with a long history is much quicker: items already stored are no longer written again on every check.