Version 0.3.0: resolver/merge/cache refactor, signing design notes

- Split the monolith into package/provider/fetch/merge/cache modules with
  the Resolver deciding install/adopt/update/merge/conflict outcomes
- Three-way merges via git merge-file/diff3 against a content-addressed
  merge-base cache; conflicts go to a .picopackage-merge sibling
- Tests for package, provider, resolver, merge, and cache
- notes.md: update UX and signing design — diff-by-default, SSH signature
  identity pinning (TOFU), key changes as a hard stop, exit-code contract
- Add CLAUDE.md; remove the pre-refactor exe/pppkg monolith and scratch files

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EiyJC73Mz8xZyCTvCEY8qn

test/files/uniquify_array_packaged.rb

@@ -0,0 +1,18 @@
+# Make an array of hashes contain a unique value for key:
+def uniquify_array(array, key)
+  array.group_by { |item| item[key] }.map do |_, items|
+    (items.length > 1) ? yield(items) : items.first
+  end
+end
+
+# new_array = uniquify_array(array, :some_key) do |dupes|
+#   dupes.max_by { |item| item[:updated_at] }
+# end
+
+# @PICOPACKAGE_START
+# ---
+# filename: uniquify_array.rb
+# url: https://api.github.com/gists/525ac4177964549ee2f2ca7febd03eea
+# version: 0.1
+# source_url: https://gist.github.com/dkam/525ac4177964549ee2f2ca7febd03eea
+# @PICOPACKAGE_END