feat: geo_filter enforcement, DB pruning, geofilter-builder tool, HB column (#215)

## Summary

Several features and fixes from a live deployment of the Go v3.0.0
backend.

### geo_filter — full enforcement

- **Go backend config** (`cmd/server/config.go`,
`cmd/ingestor/config.go`): added `GeoFilterConfig` struct so
`geo_filter.polygon` and `bufferKm` from `config.json` are parsed by
both the server and ingestor
- **Ingestor** (`cmd/ingestor/geo_filter.go`, `cmd/ingestor/main.go`):
ADVERT packets from nodes outside the configured polygon + buffer are
dropped *before* any DB write — no transmission, node, or observation
data is stored
- **Server API** (`cmd/server/geo_filter.go`, `cmd/server/routes.go`):
`GET /api/config/geo-filter` endpoint returns the polygon + bufferKm to
the frontend; `/api/nodes` responses filter out any out-of-area nodes
already in the DB
- **Frontend** (`public/map.js`, `public/live.js`): blue polygon overlay
(solid inner + dashed buffer zone) on Map and Live pages, toggled via
"Mesh live area" checkbox, state shared via localStorage

### Automatic DB pruning

- Add `retention.packetDays` to `config.json` to delete transmissions +
observations older than N days on a daily schedule (1 min after startup,
then every 24h). Nodes and observers are never pruned.
- `POST /api/admin/prune?days=N` for manual runs (requires `X-API-Key`
header if `apiKey` is set)

```json
"retention": {
  "nodeDays": 7,
  "packetDays": 30
}
```

### tools/geofilter-builder.html

Standalone HTML tool (no server needed) — open in browser, click to
place polygon points on a Leaflet map, set `bufferKm`, copy the
generated `geo_filter` JSON block into `config.json`.

### scripts/prune-nodes-outside-geo-filter.py

Utility script to clean existing out-of-area nodes from the database
(dry-run + confirm). Useful after first enabling geo_filter on a
populated DB.

### HB column in packets table

Shows the hop hash size in bytes (1–4) decoded from the path byte of
each packet's raw hex. Displayed as **HB** between Size and Type
columns, hidden on small screens.

## Test plan

- [x] ADVERT from node outside polygon is not stored (no new row in
nodes or transmissions)
- [x] `GET /api/config/geo-filter` returns polygon + bufferKm when
configured, `{polygon: null, bufferKm: 0}` when not
- [x] `/api/nodes` excludes nodes outside polygon even if present in DB
- [x] Map and Live pages show blue polygon overlay when configured;
checkbox toggles it
- [x] `retention.packetDays: 30` deletes old transmissions/observations
on startup and daily
- [x] `POST /api/admin/prune?days=30` returns `{deleted: N, days: 30}`
- [x] `tools/geofilter-builder.html` opens standalone, draws polygon,
copies valid JSON
- [x] HB column shows 1–4 for all packets in grouped and flat view

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/prune-nodes-outside-geo-filter.py

@@ -0,0 +1,168 @@
+#!/usr/bin/env python3
+"""
+Delete nodes from the database that fall outside the configured geo_filter polygon + bufferKm.
+Nodes with no GPS coordinates are always kept.
+
+Usage:
+  python3 prune-nodes-outside-geo-filter.py [db_path] [--config config.json] [--dry-run]
+
+  db_path         Path to meshcore.db   (default: /app/data/meshcore.db)
+  --config PATH   Path to config.json   (default: /app/config.json)
+  --dry-run       Show what would be deleted without making any changes
+"""
+
+import sqlite3
+import math
+import sys
+import json
+import os
+
+
+def point_in_polygon(lat, lon, polygon):
+    """Ray-casting algorithm."""
+    inside = False
+    n = len(polygon)
+    j = n - 1
+    for i in range(n):
+        yi, xi = polygon[i]   # lat, lon
+        yj, xj = polygon[j]
+        if ((yi > lat) != (yj > lat)) and (lon < (xj - xi) * (lat - yi) / (yj - yi) + xi):
+            inside = not inside
+        j = i
+    return inside
+
+
+def dist_to_segment_km(lat, lon, a, b):
+    """Approximate distance (km) from point to line segment, using flat-earth projection."""
+    lat1, lon1 = a
+    lat2, lon2 = b
+    mid_lat = (lat1 + lat2) / 2.0
+    cos_lat = math.cos(math.radians(mid_lat))
+    km_per_deg_lat = 111.0
+    km_per_deg_lon = 111.0 * cos_lat
+
+    # Translate so point is at origin
+    ax = (lon1 - lon) * km_per_deg_lon
+    ay = (lat1 - lat) * km_per_deg_lat
+    bx = (lon2 - lon) * km_per_deg_lon
+    by = (lat2 - lat) * km_per_deg_lat
+
+    abx, aby = bx - ax, by - ay
+    ab_sq = abx * abx + aby * aby
+    if ab_sq == 0:
+        return math.sqrt(ax * ax + ay * ay)
+
+    t = max(0.0, min(1.0, -(ax * abx + ay * aby) / ab_sq))
+    px = ax + t * abx
+    py = ay + t * aby
+    return math.sqrt(px * px + py * py)
+
+
+def node_passes_filter(lat, lon, polygon, buffer_km):
+    """Return True if the node should be kept."""
+    if lat is None or lon is None:
+        return True
+    if lat == 0.0 and lon == 0.0:
+        return True  # no GPS fix
+    if point_in_polygon(lat, lon, polygon):
+        return True
+    if buffer_km > 0:
+        n = len(polygon)
+        for i in range(n):
+            j = (i + 1) % n
+            if dist_to_segment_km(lat, lon, polygon[i], polygon[j]) <= buffer_km:
+                return True
+    return False
+
+
+def load_geo_filter(config_path):
+    """Load polygon and bufferKm from config.json geo_filter section."""
+    if not os.path.exists(config_path):
+        print(f"ERROR: config not found at {config_path}")
+        sys.exit(1)
+    with open(config_path) as f:
+        cfg = json.load(f)
+    gf = cfg.get('geo_filter')
+    if not gf:
+        print("ERROR: no geo_filter section found in config.json")
+        sys.exit(1)
+    polygon = gf.get('polygon', [])
+    if len(polygon) < 3:
+        print("ERROR: geo_filter.polygon must have at least 3 points")
+        sys.exit(1)
+    buffer_km = gf.get('bufferKm', 0.0)
+    print(f"Loaded geo_filter from {config_path}: {len(polygon)} points, bufferKm={buffer_km}")
+    return polygon, buffer_km
+
+
+def main():
+    args = sys.argv[1:]
+    dry_run = '--dry-run' in args
+    args = [a for a in args if a != '--dry-run']
+
+    config_path = '/app/config.json'
+    if '--config' in args:
+        idx = args.index('--config')
+        config_path = args[idx + 1]
+        args = args[:idx] + args[idx + 2:]
+
+    db_path = args[0] if args else '/app/data/meshcore.db'
+
+    polygon, buffer_km = load_geo_filter(config_path)
+
+    if not os.path.exists(db_path):
+        print(f"ERROR: database not found at {db_path}")
+        sys.exit(1)
+
+    conn = sqlite3.connect(db_path)
+    conn.row_factory = sqlite3.Row
+    cur = conn.cursor()
+
+    cur.execute('SELECT public_key, name, lat, lon FROM nodes ORDER BY name')
+    nodes = cur.fetchall()
+
+    keep, remove = [], []
+    for row in nodes:
+        lat = row['lat']
+        lon = row['lon']
+        if node_passes_filter(lat, lon, polygon, buffer_km):
+            keep.append(row)
+        else:
+            remove.append(row)
+
+    print(f"Total nodes in DB : {len(nodes)}")
+    print(f"Nodes to keep     : {len(keep)}")
+    print(f"Nodes to delete   : {len(remove)}")
+
+    if not remove:
+        print("\nNothing to delete.")
+        conn.close()
+        return
+
+    print("\nNodes that will be DELETED:")
+    for row in remove:
+        lat = row['lat'] or 0
+        lon = row['lon'] or 0
+        name = row['name'] or row['public_key'][:12]
+        print(f"  {name:<30}  lat={lat:.4f}  lon={lon:.4f}")
+
+    if dry_run:
+        print("\n[dry-run] No changes made.")
+        conn.close()
+        return
+
+    confirm = input(f"\nDelete {len(remove)} nodes? Type 'yes' to confirm: ").strip()
+    if confirm.lower() != 'yes':
+        print("Aborted.")
+        conn.close()
+        return
+
+    pubkeys = [row['public_key'] for row in remove]
+    cur.executemany('DELETE FROM nodes WHERE public_key = ?', [(pk,) for pk in pubkeys])
+    conn.commit()
+    print(f"\nDeleted {cur.rowcount if cur.rowcount >= 0 else len(pubkeys)} nodes.")
+    conn.close()
+
+
+if __name__ == '__main__':
+    main()