lazyflat: combined alert + apply behind authenticated web UI

Three isolated services (alert scraper, apply HTTP worker, web UI+DB)
with argon2 auth, signed cookies, CSRF, rate-limited login, kill switch,
apply circuit breaker, audit log, and strict CSP.

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

apply/providers/_provider.py

@@ -0,0 +1,22 @@
+import asyncio
+from abc import ABC, abstractmethod
+import logging
+
+from classes.application_result import ApplicationResult
+
+logger = logging.getLogger("flat-apply")
+
+class Provider(ABC):
+    @property
+    @abstractmethod
+    def domain(self) -> str:
+        """every flat provider needs a domain"""
+        pass
+
+    @abstractmethod
+    async def apply_for_flat(self, url: str) -> ApplicationResult:
+        """every flat provider needs to be able to apply for flats"""
+        pass
+
+    def test_apply(self, url):
+        print(asyncio.run(self.apply_for_flat(url)))