Add horoscope, !time @user, profile achievements; fix mention detection and multiple bugs

- Add !horoscope command and daily horoscope digest using Free Horoscope API
- Enhance !time to support @user timezone lookups
- Add profile completeness achievements (birthday, timezone, both set)
- Fix Matrix mention detection in reputation and LLM passive plugins
- Fix !whois reputation query (reason string mismatch and calculation)
- Fix !time IANA case-sensitivity and username/city collision
- Fix timezone default to empty string for achievement detection
- Scope all leaderboards to room members (XP, rep, potty, insult, first, rankings, emoji)
- Fix XP rank calculation to handle tied scores correctly
- Replace skull emoji with bomb for bot insult reactions

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/plugin/birthday.go

@@ -95,7 +95,7 @@ func (p *BirthdayPlugin) handleSet(ctx MessageContext, dateStr string) error {
 
 	d := db.Get()
 	_, err = d.Exec(
-		`INSERT INTO birthdays (user_id, month, day, year, timezone) VALUES (?, ?, ?, ?, 'UTC')
+		`INSERT INTO birthdays (user_id, month, day, year) VALUES (?, ?, ?, ?)
 		 ON CONFLICT(user_id) DO UPDATE SET month = ?, day = ?, year = ?`,
 		string(ctx.Sender), month, day, year, month, day, year,
 	)