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>

README.md

@@ -147,7 +147,7 @@ Initiale DB-Settings (Seed):
 - Geschaeftslogik bleibt in Services.
 - `pages/.../*.php` fungiert als Action-/Controller-Schicht.
 - Service-Aufloesung in Actions/Helpern ueber `app(Foo::class)`.
-- `new ...Factory()` nur im Composition Root (`web/index.php` + `lib/App/registerContainer.php`) oder in `*Factory.php`.
+- `new ...Factory()` nur im Composition Root (`web/index.php` + `core/App/registerContainer.php`) oder in `*Factory.php`.
 - `pages/**/data().php` sind GET-only (`gridRequireGetRequest()`) und normalisieren `limit`/`offset`/`order`/`dir` ueber Grid-Helper.
 - Permissions + Tenant-Scope werden in Actions/Services erzwungen.
 - Wiederkehrende UI-Bloecke als Partials zentralisieren.