[feat](trx-frontend-http): add FM broadcast band (87.5-108 MHz) to bandplan

Add the FM broadcasting band to all three IARU regions so the
87.5-108 MHz range is visible in the bandplan overlay.

https://claude.ai/code/session_01XCmCtBud7riY5anZRvvK2p
Signed-off-by: Claude <noreply@anthropic.com>

src/trx-client/trx-frontend/trx-frontend-http/assets/web/bandplan.json

@@ -122,6 +122,12 @@
           { "low_hz": 70300000, "high_hz": 70500000, "mode": "FM", "label": "FM" }
         ]
       },
+      {
+        "name": "FM Broadcast", "low_hz": 87500000, "high_hz": 108000000,
+        "segments": [
+          { "low_hz": 87500000, "high_hz": 108000000, "mode": "FM", "label": "FM Broadcasting" }
+        ]
+      },
       {
         "name": "2m", "low_hz": 144000000, "high_hz": 146000000,
         "segments": [
@@ -274,6 +280,12 @@
           { "low_hz": 51000000, "high_hz": 54000000, "mode": "FM", "label": "FM" }
         ]
       },
+      {
+        "name": "FM Broadcast", "low_hz": 87500000, "high_hz": 108000000,
+        "segments": [
+          { "low_hz": 87500000, "high_hz": 108000000, "mode": "FM", "label": "FM Broadcasting" }
+        ]
+      },
       {
         "name": "2m", "low_hz": 144000000, "high_hz": 148000000,
         "segments": [
@@ -438,6 +450,12 @@
           { "low_hz": 51000000, "high_hz": 54000000, "mode": "FM", "label": "FM" }
         ]
       },
+      {
+        "name": "FM Broadcast", "low_hz": 87500000, "high_hz": 108000000,
+        "segments": [
+          { "low_hz": 87500000, "high_hz": 108000000, "mode": "FM", "label": "FM Broadcasting" }
+        ]
+      },
       {
         "name": "2m", "low_hz": 144000000, "high_hz": 148000000,
         "segments": [