refactor: rename wohnungsdidi → lazyflat

Container names, FastAPI titles, email subjects, filenames, brand text,
session cookie, User-Agent, docstrings, README. Volume lazyflat_data and
/data/lazyflat.sqlite already used the new name, so on-disk data is
preserved; dropped the now-obsolete legacy-rename comments.

Side effect: SESSION_COOKIE_NAME change logs everyone out on deploy.

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

web/routes/bewerbungen.py

@@ -43,7 +43,7 @@ def bewerbung_zip(request: Request, app_id: int):
     with zipfile.ZipFile(buf, "w", compression=zipfile.ZIP_DEFLATED) as zf:
         zf.writestr(
             "README.txt",
-            f"wohnungsdidi application report\n"
+            f"lazyflat application report\n"
             f"application_id={a['id']}\n"
             f"flat_id={a['flat_id']}\n"
             f"provider={a['provider']}\n"
@@ -95,7 +95,7 @@ def bewerbung_zip(request: Request, app_id: int):
                 zf.writestr(f"snapshots/{idx:02d}_{label}.html", html)
 
     buf.seek(0)
-    filename = f"wohnungsdidi-report-{a['id']}.zip"
+    filename = f"lazyflat-report-{a['id']}.zip"
     return StreamingResponse(
         buf, media_type="application/zip",
         headers={"Content-Disposition": f'attachment; filename="{filename}"'},