feat: add customer-owned frontend, device config, pricing (v1.2.0)

- Add frontend/ at root (customer's own React app, all pages)
- Add customers/tianpu/devices.json (17 devices, 375kW PV)
- Add customers/tianpu/pricing.json (Beijing TOU 4-tier)
- Add customers/tianpu/hooks/__init__.py
- Add .githooks/pre-commit to block core/ modifications
- Add CLAUDE.md, .gitignore
- Update docker-compose.override.yml frontend -> ./frontend
- Pin bcrypt==4.0.1 in requirements.txt

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

.githooks/pre-commit

@@ -0,0 +1,10 @@
+#!/bin/bash
+# Pre-commit hook: block direct modifications to core/ subtree
+if git diff --cached --name-only | grep -q '^core/'; then
+  echo '=========================================='
+  echo 'ERROR: Do not modify core/ directly!'
+  echo 'Make changes in ems-core repo instead.'
+  echo 'Then run: git subtree pull --prefix=core ems-core main --squash'
+  echo '=========================================='
+  exit 1
+fi