feat(pwa): dynamic theme-color meta tags + transparent/dark mode icons

- +layout.svelte: replace Svelte logo favicon with actual InstaChef icons;
  add two <meta name="theme-color"> tags with media queries so the browser
  chrome (mobile top bar) matches --bg for light (#FFF8F5) and dark (#110510);
  add <meta name="color-scheme" content="dark light">
- manifest.json: split 'any maskable' into separate 'any' and 'maskable' entries;
  maskable uses icon-512-maskable.png (icon with 10% safe-zone padding on gradient bg)
- New icons:
  - icon-256/512.png → replaced with transparent-background versions
  - icon-256/512-transparent.png → white bg removed via flood-fill BFS
  - icon-256/512-dark.png → transparent icon on brand gradient (#833AB4→#E1306C)
  - icon-512-maskable.png → 80% icon centered on gradient (PWA maskable safe zone)
  - favicon-32.png → 32x32 transparent icon for browser tab
  - favicon.png (192×192) → updated to transparent InstaChef icon

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

static/manifest.json

@@ -11,13 +11,19 @@
       "src": "/favicon.png",
       "sizes": "192x192",
       "type": "image/png",
-      "purpose": "any maskable"
+      "purpose": "any"
     },
     {
       "src": "/icon-512.png",
       "sizes": "512x512",
       "type": "image/png",
-      "purpose": "any maskable"
+      "purpose": "any"
+    },
+    {
+      "src": "/icon-512-maskable.png",
+      "sizes": "512x512",
+      "type": "image/png",
+      "purpose": "maskable"
     }
   ],
   "share_target": {