add CI pipeline with credo and dialyzer

mix ci alias: compile --warning-as-errors, format --check-formatted,
credo, dialyzer, test. Credo configured with sensible defaults.
Dialyzer ignore file for false positives (Stripe types, Mix tasks,
ExUnit internals). Credo fixes: map_join, filter consolidation,
nesting extraction, cond→if simplification.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/mix/tasks/generate_mockups.ex

@@ -129,7 +129,7 @@ defmodule Mix.Tasks.GenerateMockups do
 
     case MockupGenerator.search_blueprints(term) do
       results when is_list(results) ->
-        if length(results) == 0 do
+        if results == [] do
           Mix.shell().info("No blueprints found matching '#{term}'")
         else
           Mix.shell().info("\nMatching Blueprints:\n")