rename to wohnungsdidi + didi logo + footer for all + seconds-only counter

- App is now called "wohnungsdidi" everywhere user-facing (page title,
  nav brand, login header, notification subjects, report filename,
  FastAPI titles, log messages)
- Brand dot replaced with an image of Didi (web/static/didi.webp),
  rendered as a round 2.25rem avatar in _layout + login
- "Programmiert für Annika ♥" footer now shows for every logged-in user,
  not only Annika
- Count-up shows only seconds ("vor 73 s") regardless of age — no
  rollover to minutes/hours
- Data continuity: DB file stays /data/lazyflat.sqlite and the Docker
  volume stays lazyflat_data so the rename doesn't strand existing data
- Session cookie renamed to wohnungsdidi_session (one-time logout on
  rollout)

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

web/app.py

@@ -1,5 +1,5 @@
 """
-lazyflat web app.
+wohnungsdidi web app.
 
 Tabs:
 - /                           → Wohnungen
@@ -84,7 +84,7 @@ async def lifespan(_app: FastAPI):
     yield
 
 
-app = FastAPI(lifespan=lifespan, title="lazyflat", docs_url=None, redoc_url=None, openapi_url=None)
+app = FastAPI(lifespan=lifespan, title="wohnungsdidi", docs_url=None, redoc_url=None, openapi_url=None)
 app.mount("/static", StaticFiles(directory="static"), name="static")
 templates = Jinja2Templates(directory="templates")
 
@@ -712,7 +712,7 @@ def bewerbung_zip(request: Request, app_id: int):
     with zipfile.ZipFile(buf, "w", compression=zipfile.ZIP_DEFLATED) as zf:
         zf.writestr(
             "README.txt",
-            f"lazyflat application report\n"
+            f"wohnungsdidi application report\n"
             f"application_id={a['id']}\n"
             f"flat_id={a['flat_id']}\n"
             f"provider={a['provider']}\n"
@@ -764,7 +764,7 @@ def bewerbung_zip(request: Request, app_id: int):
                 zf.writestr(f"snapshots/{idx:02d}_{label}.html", html)
 
     buf.seek(0)
-    filename = f"lazyflat-report-{a['id']}.zip"
+    filename = f"wohnungsdidi-report-{a['id']}.zip"
     return StreamingResponse(
         buf, media_type="application/zip",
         headers={"Content-Disposition": f'attachment; filename="{filename}"'},
@@ -889,7 +889,7 @@ def tab_logs_export(request: Request):
             e["ip"],
         ])
     body = buf.getvalue().encode("utf-8")
-    filename = "lazyflat-protokoll"
+    filename = "wohnungsdidi-protokoll"
     if q.get("from"): filename += f"-{q['from']}"
     if q.get("to"):   filename += f"-bis-{q['to']}"
     filename += ".csv"