fix: District settings read per field, so DISTRICT_* always wins

A leftover v1 MOVIE_CODE used to switch the whole District block to the old names,
silently discarding DISTRICT_CONTENT_ID even when it was set deliberately. The
monitor then watched the wrong film and still reported 'closed', which is the
failure mode this project exists to avoid.

Each field now prefers the DISTRICT_* value and falls back to its v1 name, an
explicitly emptied value is respected, and any v1 name still in use is warned
about at startup. District is enabled by DISTRICT_CONTENT_ID rather than the
movie code, which is optional: District answers without it, and a film with no
showtimes yet has none.

.env.example

@@ -18,11 +18,13 @@ NTFY_URL=https://ntfy.sh
 # NTFY_TOKEN=tk_...            # only if your server (or topic) requires auth
 
 # ── District (district.in) ────────────────────────────────────────────────────
-# Leave DISTRICT_MOVIE_CODE unset to skip District entirely.
+# Leave DISTRICT_CONTENT_ID unset to skip District entirely.
 # Read these off the movie's page URL, e.g.
 # district.in/movies/the-odyssey-movie-tickets-in-ahmedabad-MV187151?frmtid=y7EZNLXN5Y
-DISTRICT_MOVIE_CODE=y7EZNLXN5Y       # ?frmtid= — identifies movie + language
-DISTRICT_CONTENT_ID=187151           # digits after MV
+DISTRICT_CONTENT_ID=187151           # digits after MV; this is what enables District
+DISTRICT_MOVIE_CODE=y7EZNLXN5Y       # optional ?frmtid=, pins one language/format variant.
+                                     # Leave empty for a film with no showtimes yet, since
+                                     # District only publishes the code once shows exist.
 DISTRICT_CITY_KEY=ahmedabad          # city slug in the path
 DISTRICT_LAT=23.033938956712916      # any coordinates in that city; the API needs them
 DISTRICT_LNG=72.57696301365426