chore: install refactoring guardrails (Phase 0) [guardrail-change]

- scripts/check-loc.sh: LOC budget checker (500 LOC hard cap)
- .claude/rules/architecture.md: split triggers, patterns per language
- .claude/rules/loc-exceptions.txt: documented escape hatches
- AGENTS.python.md: FastAPI conventions (routes thin, service layer)
- AGENTS.go.md: Go/Gin conventions (handler ≤40 LOC)
- AGENTS.typescript.md: Next.js conventions (page.tsx ≤250 LOC, colocation)
- CLAUDE.md extended with guardrail section + commit markers

273 files currently exceed 500 LOC — to be addressed phase by phase.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.claude/rules/loc-exceptions.txt

@@ -0,0 +1,20 @@
+# LOC Exceptions — BreakPilot Lehrer
+# Format: <glob> | owner=<person> | reason=<why> | review=<date>
+#
+# Jede Ausnahme braucht Begruendung und Review-Datum.
+# Temporaere Ausnahmen muessen mit [guardrail-change] Commit-Marker versehen werden.
+
+# Generated / Build Artifacts
+**/node_modules/** | owner=infra | reason=npm packages | review=permanent
+**/.next/** | owner=infra | reason=Next.js build output | review=permanent
+**/__pycache__/** | owner=infra | reason=Python bytecode | review=permanent
+**/venv/** | owner=infra | reason=Python virtualenv | review=permanent
+
+# Test-Dateien (duerfen groesser sein fuer Table-Driven Tests)
+**/tests/test_cv_vocab_pipeline.py | owner=klausur | reason=umfangreiche OCR Pipeline Tests | review=2026-07-01
+**/tests/test_rbac.py | owner=klausur | reason=RBAC Test-Matrix | review=2026-07-01
+**/tests/test_grid_editor_api.py | owner=klausur | reason=Grid Editor Integrationstests | review=2026-07-01
+
+# Legacy — TEMPORAER bis Refactoring abgeschlossen
+# Dateien hier werden Phase fuer Phase abgearbeitet und entfernt.
+# KEINE neuen Ausnahmen ohne [guardrail-change] Commit-Marker!