Schedule poll/notify and the digest as systemd timers

news-cycle.timer runs poll then notify every 15 minutes; news-digest.timer runs
the briefing at 08:45 daily. Both enabled and verified: a manual cycle fetched
1047 items, embedded 95 new ones and clustered them in 74s.

Units are installed as COPIES rather than symlinks. The previous service's units
were symlinked into docs/projects/news/deploy/, and when that repo was renamed
to news_triage they became dangling and the timer failed every ten minutes,
unnoticed, until this rebuild found it. Copying costs a re-copy after editing;
symlinking cost days of silent failure.

Deliberate details: the poll ExecStart is `-` prefixed so a failed fetch does not
skip notify; RandomizedDelaySec spreads polling off the quarter hour rather than
hitting 56 sources at once; the digest is Persistent so a machine that was off
at 08:45 still sends rather than skipping the day.

deploy/news-cycle.timer

@@ -0,0 +1,13 @@
+[Unit]
+Description=news: run a poll/notify cycle every 15 minutes
+
+[Timer]
+OnBootSec=3min
+OnUnitActiveSec=15min
+# Feeds are polled by many people on the quarter hour; spread the load and stay
+# a good citizen. Also avoids every source being hit at the same instant.
+RandomizedDelaySec=90
+AccuracySec=30s
+
+[Install]
+WantedBy=timers.target