Calls syncChallengeCalendarFromSheet with your X-API-Key: this must match the dashboard / PandaSuite HTTPS secret (same value as PANDASUITE_API_KEY on the function) — not the Firebase Web API key (AIza…) from the PandaSuite Firebase Session block. Sent only over HTTPS; stored in this browser's localStorage when you change fields. See community/CHALLENGE_CALENDAR_SYNC.md. Use Dry run first. Range should start at row 2 (e.g. 'Monthly Challenges'!A2:Z400) so row 1 is headers only. Extra columns through Z are stored under sheetExtras on each day (no new code per column).