refactor: export full Gregorian range, add timezone fallback, cleanup rate limit, configurable schema path

- GenerateMonthlyReport now takes explicit Gregorian start/end range,
  computed via monthGregorianRange, so Jalali/Hijri months spanning
  two Gregorian months are fully covered in exports.
- Added loadLocation helper (UTC fallback on error) and replaced all
  11 ignored-error call sites in handlers + export.
- Added periodicCleanup goroutine in NewHandler to prevent unbounded
  growth of the rateLimit map.
- schemaPath is now read from SCHEMA_PATH env var (init), defaulting
  to /app/db/schema.sql.
- Migrated sendDayView to use sendOrEdit helper, removing duplicated
  send/edit branching.
- Removed dead code: userYearMonthToGregorian (unused), the old
  startOffset function (replaced).
- Updated README with calendar docs, new env vars, full project tree.
- Updated .env.example and docker-compose.yml with SCHEMA_PATH.
- Simplified Makefile: added fmt, tidy, check, run-dev targets;
  removed broken Make-glob prerequisite pattern.

docker-compose.yml

@@ -12,6 +12,7 @@ services:
       - HTTP_PROXY=${HTTP_PROXY-}
       - HTTPS_PROXY=${HTTPS_PROXY-}
       - DB_PATH=/data/db.sqlite3
+      - SCHEMA_PATH=${SCHEMA_PATH:-/app/db/schema.sql}
       - TZ=Asia/Tehran
     volumes:
       - worktime_data:/data