v0.9.12: archive-level monitoring-area bbox filter

Add a single archive-level geographic filter at the events INSERT path: events
whose geometry falls entirely outside a system-configured monitoring area are
dropped before archival. Null-geom events (SWPC trio, .removed tombstones) are
always kept. Uses a pure shapely intersects() predicate so border-straddlers
are kept (matches ST_Intersects), and is fail-open on unparseable geometry.

- config.system gains monitor_{north,south,east,west} (migration 030, Idaho default)
- archive refreshes the bbox every 60s (no restart needed to change it); adds a
  per-adapter dropped-count counter, debug log per drop, cumulative INFO rollup
- new GUI editor at /monitoring-area (Leaflet draggable rectangle, N/S/E/W inputs)
- no adapter code changes; well-behaved adapters keep upstream API filtering
- 12 tests covering all five verdicts, drop-and-count, border/point-on-edge, fail-open

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

sql/migrations/030_add_monitoring_area.sql

@@ -0,0 +1,10 @@
+-- Migration 030: Add system-level monitoring-area bbox to config.system (v0.9.12)
+-- Backs the archive-level safety-net filter: events whose geometry lies entirely
+-- outside this bbox are dropped at INSERT time; null-geom events are always kept.
+-- Default bounds = Idaho. Idempotent per docs/migrations.md.
+
+ALTER TABLE config.system
+    ADD COLUMN IF NOT EXISTS monitor_north DOUBLE PRECISION NOT NULL DEFAULT 44.5,
+    ADD COLUMN IF NOT EXISTS monitor_south DOUBLE PRECISION NOT NULL DEFAULT 41.8,
+    ADD COLUMN IF NOT EXISTS monitor_east  DOUBLE PRECISION NOT NULL DEFAULT -111.0,
+    ADD COLUMN IF NOT EXISTS monitor_west  DOUBLE PRECISION NOT NULL DEFAULT -117.5;