Expose which search strategy produced each result

query_packages now assigns @search_sources - a hash mapping package
ids to the matching strategy that put them into the results: :exact,
:name_prefix, :name_contains, :semantic or :fulltext. The grid and
list views render a small badge with a humanized label per result,
making the search tiers observable. semantic_results() was folded
into search_packages() so each branch tags its own source. Adds the
rails-controller-testing gem for assigns() in tests.

Gemfile

@@ -108,6 +108,8 @@ group :test do
   # Use system testing [https://guides.rubyonrails.org/testing.html#system-testing]
   gem 'capybara'
   gem 'selenium-webdriver'
+  # Provides the assigns() test helper extracted from modern Rails
+  gem 'rails-controller-testing'
 end
 
 # TODO… https://github.com/galetahub/simple-captcha