Backlog, tests, logo compression, security audit, App Store icon

- BACKLOG.md: P0-P3 roadmap incl. govuk API switch (blocked on credentials)
- APPSTORE.md: review-gate analysis (2 blockers: LAN data source, Always-location notes)
- SECURITY.md: audit - no secrets, no ATS holes, one MEDIUM (relay IP in binary, planned fix)
- FuelBoardTests/: SPM package, 28 tests on real Shared/ sources (sanitizer, price guard, RAG, sort, distance, brands)
- Logos: proper 2x/3x pairs, palette-quantized, 75% smaller (315KB -> 79KB)
- App icon: 1024px fuelpump on gradient (was missing entirely -> instant rejection)
- decodeStations(from:) exposed for testability; relay fetch reuses it

FuelBoard/Assets.xcassets/AppIcon.appiconset/Contents.json

@@ -0,0 +1,14 @@
+{
+  "images" : [
+    {
+      "filename" : "AppIcon.png",
+      "idiom" : "universal",
+      "platform" : "ios",
+      "size" : "1024x1024"
+    }
+  ],
+  "info" : {
+    "author" : "xcode",
+    "version" : 1
+  }
+}

FuelBoard/Assets.xcassets/brand_applegreen.imageset/Contents.json

@@ -1,9 +1,14 @@
 {
   "images": [
     {
-      "filename": "brand_applegreen.png",
+      "filename": "brand_applegreen_2x.png",
       "idiom": "universal",
       "scale": "2x"
+    },
+    {
+      "filename": "brand_applegreen_3x.png",
+      "idiom": "universal",
+      "scale": "3x"
     }
   ],
   "info": {

FuelBoard/Assets.xcassets/brand_asda.imageset/Contents.json

@@ -1,9 +1,14 @@
 {
   "images": [
     {
-      "filename": "brand_asda.png",
+      "filename": "brand_asda_2x.png",
       "idiom": "universal",
       "scale": "2x"
+    },
+    {
+      "filename": "brand_asda_3x.png",
+      "idiom": "universal",
+      "scale": "3x"
     }
   ],
   "info": {

FuelBoard/Assets.xcassets/brand_bp.imageset/Contents.json

@@ -1,9 +1,14 @@
 {
   "images": [
     {
-      "filename": "brand_bp.png",
+      "filename": "brand_bp_2x.png",
       "idiom": "universal",
       "scale": "2x"
+    },
+    {
+      "filename": "brand_bp_3x.png",
+      "idiom": "universal",
+      "scale": "3x"
     }
   ],
   "info": {

FuelBoard/Assets.xcassets/brand_esso.imageset/Contents.json

@@ -1,9 +1,14 @@
 {
   "images": [
     {
-      "filename": "brand_esso.png",
+      "filename": "brand_esso_2x.png",
       "idiom": "universal",
       "scale": "2x"
+    },
+    {
+      "filename": "brand_esso_3x.png",
+      "idiom": "universal",
+      "scale": "3x"
     }
   ],
   "info": {

FuelBoard/Assets.xcassets/brand_gulf.imageset/Contents.json

@@ -1,9 +1,14 @@
 {
   "images": [
     {
-      "filename": "brand_gulf.png",
+      "filename": "brand_gulf_2x.png",
       "idiom": "universal",
       "scale": "2x"
+    },
+    {
+      "filename": "brand_gulf_3x.png",
+      "idiom": "universal",
+      "scale": "3x"
     }
   ],
   "info": {

FuelBoard/Assets.xcassets/brand_jet.imageset/Contents.json

@@ -1,9 +1,14 @@
 {
   "images": [
     {
-      "filename": "brand_jet.png",
+      "filename": "brand_jet_2x.png",
       "idiom": "universal",
       "scale": "2x"
+    },
+    {
+      "filename": "brand_jet_3x.png",
+      "idiom": "universal",
+      "scale": "3x"
     }
   ],
   "info": {

FuelBoard/Assets.xcassets/brand_morrisons.imageset/Contents.json

@@ -1,9 +1,14 @@
 {
   "images": [
     {
-      "filename": "brand_morrisons.png",
+      "filename": "brand_morrisons_2x.png",
       "idiom": "universal",
       "scale": "2x"
+    },
+    {
+      "filename": "brand_morrisons_3x.png",
+      "idiom": "universal",
+      "scale": "3x"
     }
   ],
   "info": {

FuelBoard/Assets.xcassets/brand_sainsburys.imageset/Contents.json

@@ -1,9 +1,14 @@
 {
   "images": [
     {
-      "filename": "brand_sainsburys.png",
+      "filename": "brand_sainsburys_2x.png",
       "idiom": "universal",
       "scale": "2x"
+    },
+    {
+      "filename": "brand_sainsburys_3x.png",
+      "idiom": "universal",
+      "scale": "3x"
     }
   ],
   "info": {

FuelBoard/Assets.xcassets/brand_shell.imageset/Contents.json

@@ -1,9 +1,14 @@
 {
   "images": [
     {
-      "filename": "brand_shell.png",
+      "filename": "brand_shell_2x.png",
       "idiom": "universal",
       "scale": "2x"
+    },
+    {
+      "filename": "brand_shell_3x.png",
+      "idiom": "universal",
+      "scale": "3x"
     }
   ],
   "info": {

FuelBoard/Assets.xcassets/brand_tesco.imageset/Contents.json

@@ -1,9 +1,14 @@
 {
   "images": [
     {
-      "filename": "brand_tesco.png",
+      "filename": "brand_tesco_2x.png",
       "idiom": "universal",
       "scale": "2x"
+    },
+    {
+      "filename": "brand_tesco_3x.png",
+      "idiom": "universal",
+      "scale": "3x"
     }
   ],
   "info": {

FuelBoard/Assets.xcassets/brand_texaco.imageset/Contents.json

@@ -1,9 +1,14 @@
 {
   "images": [
     {
-      "filename": "brand_texaco.png",
+      "filename": "brand_texaco_2x.png",
       "idiom": "universal",
       "scale": "2x"
+    },
+    {
+      "filename": "brand_texaco_3x.png",
+      "idiom": "universal",
+      "scale": "3x"
     }
   ],
   "info": {