Series return number of installations, not users at bucket day

pluginInstallations semantics: number of installations “active” on the bucket day, defined as:

first_data_sent <= day AND day < last_data_sent + 4 weeks

• Counts cumulative installations within the 4-week window from the last data transmission, not “how many sent data on that day”.
• No drop-offs or re-entries are tracked: installing on Monday and re-installing on Wednesday (new id) counts on both days. Intentional; traceability is not intended.