poi-index: extract pipeline (BRouter host) + import job (flagship) + e2e

- poi-extract.sh: PBF download -> osmium tags-filter -> centroid NDJSON +
  manifest, published via the Caddy sidecar at vSwitch-only /poi/*
- osmium-filters.txt + poi-selectors.sql generated from map-core selectors,
  guarded by sync tests so poiCategories stays the single source of truth
- poi-import.sh: checksum verify -> classify into category rows ->
  70% guard (--bootstrap override) -> atomic rename swap; node_exporter
  textfile metric for import outcome
- systemd service+timer units for both halves (monthly, offset)
- cd-infra.yml: ship infrastructure/scripts to the flagship
- e2e: mock /api/pois instead of /api/overpass

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

infrastructure/scripts/poi-import.timer

@@ -0,0 +1,12 @@
+# Monthly POI import, offset a day after the BRouter host's extract (which runs
+# on the 1st) so the fresh artifact is already published when this pulls it.
+[Unit]
+Description=Monthly trails.cool POI index import
+
+[Timer]
+OnCalendar=*-*-02 04:00:00
+Persistent=true
+RandomizedDelaySec=30m
+
+[Install]
+WantedBy=timers.target