chore: init wp-multi-city v0.1.0 with S1 skeleton + S2 design spec

S1 skeleton (cp-8ci, already done):
- wp-multi-city.php with header, constants, hooks bootstrap
- includes/class-plugin.php with PSR-4-ish autoloader, ACF dependency guard
- includes/class-activator.php placeholder
- composer.json (PHP 8.0, phpunit dev)
- README.md with roadmap
- uninstall.php placeholder

S2 design (cp-q7g):
- docs/superpowers/specs/2026-05-12-s2-taxonomy-cpt-acf-design.md

.gitignore

@@ -0,0 +1,9 @@
+/vendor/
+/composer.lock
+/dist/
+/.phpunit.result.cache
+/.idea/
+/.vscode/
+.DS_Store
+*.log
+*.zip