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.

internal/bot/dateutil.go

@@ -1,6 +1,9 @@
 package bot
 
-import "fmt"
+import (
+	"fmt"
+	"time"
+)
 
 var gregMonthDays = []int{31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}
 var jalaliMonthDays = []int{31, 31, 31, 31, 31, 31, 30, 30, 30, 30, 30, 29}
@@ -303,20 +306,6 @@ func userDateToGregorian(dateStr, cal string) string {
 	return fmt.Sprintf("%04d-%02d-%02d", y, m, d)
 }
 
-// userYearMonthToGregorian converts a (year, month) in the user's calendar
-// to the corresponding Gregorian (year, month). The day is assumed to be 1.
-func userYearMonthToGregorian(year, month int, cal string) (int, int) {
-	switch cal {
-	case "jalali":
-		gy, gm, _ := jalaliToGregorian(year, month, 1)
-		return gy, gm
-	case "hijri":
-		gy, gm, _ := hijriToGregorian(year, month, 1)
-		return gy, gm
-	}
-	return year, month
-}
-
 // monthGregorianRange returns the Gregorian start and end date strings
 // for a given calendar month (cal=gregorian|jalali|hijri).
 func monthGregorianRange(cal string, year, month int) (start, end string) {
@@ -340,3 +329,12 @@ func monthGregorianRange(cal string, year, month int) (start, end string) {
 	}
 	return
 }
+
+// loadLocation loads a timezone, falling back to UTC on error.
+func loadLocation(tz string) *time.Location {
+	loc, err := time.LoadLocation(tz)
+	if err != nil {
+		return time.UTC
+	}
+	return loc
+}