Make admin notification recipients configurable via ADMIN_EMAILS

Previously the To/Cc addresses were hardcoded in notifier.py (Andrea,
Barbara, Markus). This caused accidental emails to production contacts
during testing.

Changes:
- New ADMIN_EMAILS env var: comma-separated list of addresses.
  First address → To; remaining addresses → Cc.
- AdminNotifier now accepts admin_emails list; warns and skips if empty.
- Removed hardcoded _INDOOR_EMAIL / _OUTDOOR_EMAIL / _ADMIN_CC_EMAIL
  constants and the _recipients_for() routing method.
- Config.from_env() parses ADMIN_EMAILS into a list.
- main.py passes config.admin_emails to AdminNotifier.
- .env.example documents the new variable with production example.
- Tests: fixture updated; TestRecipientsFor removed (routing gone).

For testing: ADMIN_EMAILS=you@example.com
For production: ADMIN_EMAILS=andrea.sigrist@gmx.net,baba.laeubli@gmail.com,spielgruppen@familien-verein.ch

https://claude.ai/code/session_01HaUFs7SaLD5SoiuGCY27Tw

src/config.py

@@ -32,6 +32,11 @@ class Config:
     # Registration email address shown to parents
     registration_email: str = ""
 
+    # Admin notification recipients (comma-separated).
+    # First address → To; remaining addresses → Cc.
+    # Set to a single address (e.g. your own) during testing.
+    admin_emails: list = field(default_factory=list)
+
     # Storage
     data_dir: Path = field(default_factory=lambda: Path("data"))
     knowledge_base_dir: Path = field(
@@ -56,6 +61,11 @@ class Config:
             smtp_port=int(os.getenv("SMTP_PORT", "587")),
             smtp_use_tls=os.getenv("SMTP_USE_TLS", "true").lower() == "true",
             registration_email=os.getenv("REGISTRATION_EMAIL", ""),
+            admin_emails=[
+                e.strip()
+                for e in os.getenv("ADMIN_EMAILS", "").split(",")
+                if e.strip()
+            ],
             data_dir=Path(os.getenv("DATA_DIR", "data")),
             knowledge_base_dir=Path(
                 os.getenv(