chore: sweep dead code across all three services

Per review §1 — verified no callers before each deletion:

- _next_scrape_utc (context dict key never read by any template)
- ALERT_SCRAPE_INTERVAL_SECONDS settings import (only _next_scrape_utc read it)
- alert/paths.py (imported by nothing)
- alert/settings.py LANGUAGE (alert doesn't use translations.toml)
- alert/main.py: the vestigial `c = {}` connectivity dict, the comment
  about re-enabling it, and the entire connectivity block in
  _flat_payload — the web-side columns stay NULL on insert now
- alert/maps.py: DESTINATIONS, calculate_score, _get_next_weekday,
  _calculate_transfers (only geocode is used in the scraper)
- alert/flat.py: connectivity + display_address properties,
  _connectivity field, unused datetime import
- apply/utils.py str_to_preview (no callers) — file removed
- web/matching.py: max_morning_commute + commute check
- web/app.py: don't pass connectivity dict into flat_matches_filter,
  don't write email_address through update_notifications
- web/db.py: get_error (no callers); drop kill_switch,
  max_morning_commute, email_address from their allowed-sets so they're
  not writable through update_* anymore
- web/settings.py + docker-compose.yml: SMTP_HOST/PORT/USERNAME/PASSWORD/
  FROM/STARTTLS (notifications.py is telegram-only now)

DB columns themselves (kill_switch, email_address, max_morning_commute,
connectivity_morning_time, connectivity_night_time) stay in the schema
— SQLite can't drop them cheaply and they're harmless.

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

alert/main.py

@@ -31,11 +31,6 @@ class FlatAlerter:
         self.last_response_hash = ""
 
     def _flat_payload(self, flat: Flat) -> dict:
-        # Transit-connectivity is disabled to save Google-Maps quota. The
-        # helper on Flat (flat.connectivity → Maps.calculate_score) is
-        # intentionally kept so it can be re-enabled without re-writing code —
-        # just replace the empty dict with `flat.connectivity` when needed.
-        c: dict = {}
         lat, lng = flat.coords
         return {
             "id": flat.id,
@@ -60,12 +55,6 @@ class FlatAlerter:
             "address_link_gmaps": flat.address_link_gmaps,
             "lat": lat,
             "lng": lng,
-            "connectivity": {
-                "morning_time": c.get("morning_time", 0),
-                "morning_transfers": c.get("morning_transfers", 0),
-                "night_time": c.get("night_time", 0),
-                "night_transfers": c.get("night_transfers", 0),
-            },
             "raw_data": flat.raw_data,
         }