refactor: rename lib/ to core/ for clearer core-module separation

Rename the top-level lib/ directory to core/ so the project root
immediately communicates which code is core platform and which lives
in modules/. PHP namespaces (MintyPHP\*) are unchanged — only the
Composer PSR-4 path mapping moves from lib/ to core/.

Module-internal lib/ directories (modules/*/lib/) are untouched.

Updated across the full stack:
- composer.json PSR-4 mapping
- bootstrap entry points (web/index.php, bin/*, tests/bootstrap.php)
- tooling configs (phpstan.neon, phpunit.xml, php-cs-fixer)
- 26 architecture contract tests
- enforcement-policy, guard-catalog, quality-gates
- all documentation (CLAUDE.md, README, 25 docs/, .agents/skills/)
- bin/qa-extended.sh search paths
- .claude/settings.local.json permission paths

Workflow: .agents/runs/CORE-LIB-RENAME-001/ (Analyst → Planner →
Executor → Code Review (4 findings fixed) → Security Review →
Acceptance Test → Finalizer)

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

tests/Architecture/CoreStarterkitContractTest.php

@@ -63,7 +63,7 @@ class CoreStarterkitContractTest extends TestCase
         ];
 
         foreach ($patterns as $pattern => $label) {
-            $violations = $this->findPatternMatchesInPhpFiles('lib/Service', $pattern);
+            $violations = $this->findPatternMatchesInPhpFiles('core/Service', $pattern);
             $this->assertSame([], $violations, "Superglobal {$label} usage found in lib/Service/:\n" . implode("\n", $violations));
         }
     }
@@ -139,7 +139,7 @@ class CoreStarterkitContractTest extends TestCase
 
         foreach ($patterns as $pattern => $label) {
             $violations = array_merge(
-                $this->findPatternMatchesInPhpFiles('lib', $pattern),
+                $this->findPatternMatchesInPhpFiles('core', $pattern),
                 $this->findPatternMatchesInPhpFiles('pages', $pattern),
                 $this->findPatternMatchesInPhpFiles('tests', $pattern),
             );