docs(readme): fix phpunit command paths

There is no bin/phpunit (only bin/console) — the binary lives at
vendor/bin/phpunit, matching CLAUDE.md's documented commands.

README.md

@@ -175,7 +175,7 @@ docker compose up -d --build
 docker compose exec graph sh
 
 # Run tests inside the container
-docker compose exec graph php bin/phpunit
+docker compose exec graph vendor/bin/phpunit
 
 # Disable Xdebug for faster test runs
 XDEBUG_MODE=off docker compose up -d
@@ -195,16 +195,16 @@ docker compose -f docker-compose.yml up -d --build
 
 ```bash
 # Run full suite
-php bin/phpunit
+vendor/bin/phpunit
 
 # Human-readable output
-php bin/phpunit --testdox
+vendor/bin/phpunit --testdox
 
 # Single file
-php bin/phpunit tests/Unit/Service/SvgRendererTest.php
+vendor/bin/phpunit tests/Unit/Service/SvgRendererTest.php
 
 # Filter by name
-php bin/phpunit --filter it_renders
+vendor/bin/phpunit --filter it_renders
 ```
 
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