Fix streak grace period, UNO earnings, hospital UX, wordle/lottery atomicity

- Streak grace now checks LastDeathDate instead of LastActionDate (was
  suppressing streak updates for all active players)
- UNO single-player earnings use net payout (minus wager) not gross
- Hospital sends error message on save failure instead of silent no-op
- Wordle total_earned update moved into stats transaction
- Lottery ticket inserts + community pot add wrapped in single transaction
  with euro refund on failure
- Lottery fixed-tier ticket prize updated with actual prorated amount
- Added last_death_date column to adventure_characters

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

internal/db/db.go

@@ -82,6 +82,7 @@ func runMigrations(d *sql.DB) error {
 		`ALTER TABLE adventure_characters ADD COLUMN hospital_visits INTEGER NOT NULL DEFAULT 0`,
 		`ALTER TABLE adventure_characters ADD COLUMN robbie_visit_count INTEGER NOT NULL DEFAULT 0`,
 		`ALTER TABLE wordle_stats ADD COLUMN total_earned INTEGER NOT NULL DEFAULT 0`,
+		`ALTER TABLE adventure_characters ADD COLUMN last_death_date TEXT NOT NULL DEFAULT ''`,
 	}
 	for _, stmt := range columnMigrations {
 		if _, err := d.Exec(stmt); err != nil {