Automate Safari User-Agent freshness

[PortableProgrammer]

Background

The User-Agent header sent to Reddit (src/geddit.js, 20 call sites) was switched to a Safari UA in commit 26d7724 to bypass Reddit's blocking of generic fetch() UAs. As Safari/macOS versions roll forward, the UA drifts from current — the failure mode is "completely broken while waiting" because Reddit returns 403 to outdated/generic UAs.

Task 1 — Runtime configurability

• Move the UA from hard-coded constant to env var LURKER_USER_AGENT
• Current hard-coded value remains the default
• Operators can override without rebuild when Reddit's behavior changes

Task 2 — Scheduled refresh (stretch)

• GitHub Action with monthly cron schedule
• Fetches current stable Safari version from a reliable data source (Wikipedia "Safari version history" article, or Apple's macOS security release feed)
• Compares against the value pinned in the repo
• Opens a PR with the updated UA string if drift detected

Acceptance

Env var works (Task 1); if Task 2 lands, drift produces a visible PR rather than a silent failure.

Pragmatic note

A Safari UA from "anywhere in the last 2-3 years" is probably good enough to bypass Reddit's filter indefinitely — the annual-update urgency was assumed, not measured. Task 1 alone may be sufficient. Task 2 is a nice-to-have if Task 1 still leaves operators surprised by drift.