Split weathermap generation from dashboard composition

generate_weathermap.py now emits only the weathermap panel (targets +
options.weathermap) and merges it into a manually-authored dashboard base
(configs/grafana/dashboard-base.json) at a reserved slot panel, keeping
the base's gridPos so layout stays manual. The BGP sessions table,
ports/interfaces table, throughput graphs, and template variables move
out of the script entirely into that base file.

Verified zero regression: merged output is identical to the prior
generator-only output except for JSON key ordering, and all panel
queries re-validated via /api/ds/query.

Refs #52

configs/grafana/weathermap-dashboard.json

@@ -58,7 +58,6 @@
     "panels": [
       {
         "id": 1,
-        "type": "tamirsuliman-weathermap-panel",
         "title": "Fabric Weathermap",
         "gridPos": {
           "h": 24,
@@ -66,6 +65,7 @@
           "x": 0,
           "y": 0
         },
+        "type": "tamirsuliman-weathermap-panel",
         "datasource": {
           "type": "prometheus",
           "uid": "cfrlusac89se8a"