chore(setup): track config.php directly, slim README to setup checklist

config/config.php was gitignored and devs had to copy it from
config/config.php.example on every fresh clone. Since the bootstrap
config reads everything from .env via $envString() / $envInt() /
$envBool() defaults, there is nothing developer-specific in the file —
the cp step was dead ceremony.

- Remove config/config.php from .gitignore and track it directly
- Delete config/config.php.example
- Drop the example-existence + per-doc reference checks from
  bin/docs-drift-check.sh; add a legacy-pattern check that flags
  any new mention of the removed example file
- Update ConfigContractsTest to require config.php and forbid the
  example
- Clean stale references in CLAUDE.md, README.md, six docs files,
  and the core-guardrails skill

Same commit slims README down from 294 to 47 lines: one setup
checklist (now 3 commands instead of 4), the seeded login table,
the three quality-gate commands, and pointers to CLAUDE.md and
docs/index.md for everything else.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

bin/docs-drift-check.sh

@@ -27,26 +27,7 @@ check_legacy_pattern 'config/router\.php' 'Legacy docs reference to config/route
 check_legacy_pattern '\bAPP_ROUTE_DEFINITIONS\b' 'Legacy docs reference to APP_ROUTE_DEFINITIONS found'
 check_legacy_pattern '\bAPP_PUBLIC_PATHS\b' 'Legacy docs reference to APP_PUBLIC_PATHS found'
 check_legacy_pattern 'data-search-key' 'Legacy global-search aside marker (data-search-key) found'
-
-if [[ ! -f config/config.php.example ]]; then
-  echo "[FAIL] Missing setup template: config/config.php.example"
-  fail=1
-fi
-
-required_setup_docs=(
-  README.md
-  docs/howto-docker-lokal.md
-  docs/tutorial-01-erste-schritte.md
-  docs/tutorial-03-setup-und-erster-login.md
-  docs/howto-lokale-entwicklung.md
-)
-
-for doc in "${required_setup_docs[@]}"; do
-  if ! rg -q 'config/config\.php\.example' "${doc}"; then
-    echo "[FAIL] Missing setup contract reference in ${doc}: config/config.php.example"
-    fail=1
-  fi
-done
+check_legacy_pattern 'config/config\.php\.example' 'Legacy docs reference to config/config.php.example (file removed; config.php is now tracked)'
 
 if [[ ${fail} -ne 0 ]]; then
   echo "[FAIL] docs drift checks failed"