Render between the system bars deterministically; delete my inset bridge

The app sometimes drew under the status and gesture bars and sometimes
between them. Cause: Capacitor 8 ships a SystemBars plugin that already
handles insets, from a listener on the decor view, and my MainActivity
had installed another one on the WebView. Different views, so they
stacked rather than replaced each other and the result depended on which
fired last.

SystemBars switches on the viewport meta tag. With viewport-fit=cover it
passes insets through once onPageCommitVisible has checked the tag, decor
padding drops to 0 and the WebView grows 735 -> 820, leaving the page to
place itself from injected CSS vars. Without it the plugin pads the decor
view and the WebView is laid out between the bars already.

So sync-www.sh now strips viewport-fit=cover from the generated www/
(patch 5), MainActivity is an empty BridgeActivity, native.css and
native.js no longer touch insets, and bar style moves to
capacitor.config.json. No native->web handshake remains, so there is
nothing to race and no launch-time layout jump.

Verified identical across 3 cold launches, 2 resumes and an in-place
reload: h=735 padTop=8px overflowBy=0, panel 485px, pad rows 44.8px.

Costs no space: 820-45-114 and 735-8-66 both leave 661px. The bars take
the same room either way.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

capacitor.config.json

@@ -8,5 +8,11 @@
   },
   "server": {
     "androidScheme": "https"
+  },
+  "plugins": {
+    "SystemBars": {
+      "style": "DARK",
+      "insetsHandling": "css"
+    }
   }
 }