Accumulate GitHub repo-traffic into a persisted series for the monthly memo (#184)

[openipc-ai]

Part of #142 (Phase 2). Follow-up from #184 / PR #315 (Qodo finding #3).

Why

The memo (#184) pulls gh api repos/OpenIPC/{firmware,wiki}/traffic/popular/referrers (and views). GitHub only exposes a trailing 14-day window, so a single monthly pull is a point-in-time snapshot, not the month. Two things block a full-month figure:

1. The window is 14 days, so a full month needs at least two pulls stitched together (as the Write a monthly audience memo from a fixed set of numbers #184 spec itself notes: "14-day windows, so two pulls a month").
2. The memo runs on the origin host (webber-eu), which has no gh and no token, so today the section is a labelled placeholder there. It works only where a repo-scoped token exists (e.g. a maintainer machine).

What

Pull the two repos traffic on a schedule (roughly twice a month), from a machine/token that has repo access, into a small persisted series (deduping the overlapping 14-day windows). The monthly memo reads that series for a genuine month total instead of a live snapshot. Decide where the pull runs: a token installed on the origin, or a separate scheduled job that writes the series to the shared reports directory the memo already reads.

Done means

• GitHub referrers/views for OpenIPC/firmware and OpenIPC/wiki accumulated into a persisted, deduped series covering the calendar month.
• The memo reports the month from that series, not a 14-day snapshot, and no longer shows the placeholder in the scheduled run.
• Token handling documented (no token in the repo).